MS Update reports an "important" update available: Windows Internet Explorer 9 for Windows 7 for x64-based Systems.
 
I already have IE9
 
Telling it to install the update results in a "failed"
From Event Viewer
Installation Failure: Windows failed to install the following update with error 0x80070643: Windows Internet Explorer 9 for Windows 7 for x64-based Systems.
 
On the MS Update screen the error code is 9C48

I would first go here and run Fix:
http://support.microsoft.com/mats/Program_Install_and_Uninstall
 
http://support.microsoft.com/fixit/

Did you try thisyet? How to uninstall or remove Internet Explorer 9 when the standard uninstallation process does not work There's a Fix it button or you can do it yourself.

Let me fix it myself
To uninstall Internet Explorer 9, follow these steps: 

1. Log on to the computer as an Administrator or with an account that has administrative rights.
2. Close all Internet Explorer browser windows.
3. Click Start, type cmd in the Search box and then click cmd.exe from the programs list.
4. Copy the following command and then right-click inside the command window, click Paste, and then press Enter on the keyboard. 
   
   FORFILES /P %WINDIR%\servicing\Packages /M Microsoft-Windows-InternetExplorer-*9.*.mum /c "cmd /c echo Uninstalling package @fname && start /w pkgmgr /up:@fname /norestart"
5. Restart the computer to complete the uninstall of Internet Explorer 9.
   
   Note: When you uninstall Internet Explorer 9, the previously installed version of Internet Explorer is installed. If the previous version of Internet Explorer is not Internet Explorer 8, you can install and then configure Internet Explorer 8 from the following Microsoft website: Download Internet Explorer 8

 
A copy of the Windowsupdate.log might help troubleshoot if you still have problems.  Troubleshoot problems when you cannot install Internet Explorer 9

Disable UAC and/or try it in safe mode.
 
Here's some other options: http://superuser.com/questions/258421/how-do-i-uninstall-ie9-if-it-is-half-installed-and-not-on-the-uninstall-programs
 
Call the devil and ask if he knows any tricks. https://support.microsoft.com/oas/default.aspx?&ln=en&gprid=15672&st=1&wfxredirect=1&sd=gn
"No charge telephone support is available for install and uninstall issues. You may also be eligible for telephone support if your issue causes your computer to crash or if Internet Explorer 9 does not let you browse all sites. To learn more about your support options, please contact Microsoft at the following telephone number: (800) 642-7676"

Any idea if this is relevant (see bold):
2012-03-09    19:31:18:502    1020    758    AU    Launched new AU client for directive 'Install Approval', session id = 0x1
2012-03-09    19:31:18:549    5096    13ec    Misc    ===========  Logging initialized (build: 7.5.7601.17514, tz: -0500)  ===========
2012-03-09    19:31:18:549    5096    13ec    Misc      = Process: C:\Windows\system32\wuauclt.exe
2012-03-09    19:31:18:549    5096    13ec    AUClnt    Launched Client UI process
2012-03-09    19:31:18:736    5096    13ec    Misc    ===========  Logging initialized (build: 7.5.7601.17514, tz: -0500)  ===========
2012-03-09    19:31:18:736    5096    13ec    Misc      = Process: C:\Windows\system32\wuauclt.exe
2012-03-09    19:31:18:736    5096    13ec    Misc      = Module: C:\Windows\system32\wucltux.dll
2012-03-09    19:31:18:736    5096    13ec    CltUI    AU client got new directive = 'Install Approval', serviceId = {7971F918-A847-4430-9279-4A52D1EFE18D}, return = 0
2012-03-09    19:31:23:089    1020    758    AU    AU received handle event
2012-03-09    19:31:23:089    1020    758    AU    AU setting pending client directive to 'Install Approval'
2012-03-09    19:31:26:853    1020    758    Shutdwn    user approved update at shutdown
2012-03-09    19:31:26:853    1020    758    AU    AU found 1 updates to install at shutdown.
2012-03-09    19:31:26:853    1020    758    AU    #############
2012-03-09    19:31:26:853    1020    758    AU    ## START ##  AU: Install updates
2012-03-09    19:31:26:853    1020    758    AU    #########
2012-03-09    19:31:26:853    1020    758    AU      # Initiating install at shutdown
2012-03-09    19:31:26:853    1020    758    AU      # Approved updates = 1
2012-03-09    19:31:26:885    1020    758    AU    <<## SUBMITTED ## AU: Install updates / installing updates [CallId = {09072B62-42B6-43E5-9319-ABEC0F05A2B6}]
2012-03-09    19:31:26:885    1020    758    Shutdwn    InstallAtShutdown starts.
2012-03-09    19:31:26:885    1020    129c    Agent    *************
2012-03-09    19:31:26:885    1020    129c    Agent    ** START **  Agent: Installing updates [CallerId = AutomaticUpdates]
2012-03-09    19:31:26:885    1020    129c    Agent    *********
2012-03-09    19:31:26:885    1020    129c    Agent      * Updates to install = 1
2012-03-09    19:31:26:947    1020    129c    Agent      *   Title = Windows Internet Explorer 9 for Windows 7 for x64-based Systems
2012-03-09    19:31:26:947    1020    129c    Agent      *   UpdateId = {C6CA5181-DDA8-4506-8DE2-40957F118C8C}.101
2012-03-09    19:31:26:947    1020    129c    Agent      *     Bundles 1 updates:
2012-03-09    19:31:26:947    1020    129c    Agent      *       {565683DD-18B4-4BCB-A6AF-7F7323586782}.101
2012-03-09    19:31:27:883    1020    129c    Agent    WARNING: Failed to evaluate Installed rule, updateId = {DB5BCE37-C64D-4294-A895-17B23912A242}.101, hr = 800B0100
2012-03-09    19:31:27:930    1020    129c    Agent    WARNING: Failed to evaluate Installed rule, updateId = {818701AF-1182-45C2-BD1E-17068AD171D6}.101, hr = 80242013
2012-03-09    19:31:27:992    1020    129c    Agent    WARNING: Failed to evaluate Installed rule, updateId = {565683DD-18B4-4BCB-A6AF-7F7323586782}.101, hr = 800B0100
2012-03-09    19:31:28:039    1020    129c    Agent    WARNING: Failed to evaluate Installable rule, updateId = {EE639AA5-7BD1-49D8-B6D9-1FC80B24B490}.101, hr = 800B0100
2012-03-09    19:31:28:055    1020    1348    Shutdwn    InstallAtShutdown got install progress.
2012-03-09    19:31:38:928    1020    758    AU    WARNING: Pending directive, 'Install Approval', is not applicable
2012-03-09    19:31:41:143    1020    1348    Shutdwn    InstallAtShutdown got install progress.
2012-03-09    19:31:41:205    1020    1348    Shutdwn    InstallAtShutdown got install progress.
2012-03-09    19:31:41:205    1020    129c    DnldMgr    Preparing update for install, updateId = {565683DD-18B4-4BCB-A6AF-7F7323586782}.101.
2012-03-09    19:31:43:140    5028    124c    Misc    ===========  Logging initialized (build: 7.5.7601.17514, tz: -0500)  ===========
2012-03-09    19:31:43:140    5028    124c    Misc      = Process: C:\Windows\system32\wuauclt.exe
2012-03-09    19:31:43:140    5028    124c    Misc      = Module: C:\Windows\system32\wuaueng.dll
2012-03-09    19:31:43:140    5028    124c    Handler    :::::::::::::
2012-03-09    19:31:43:140    5028    124c    Handler    :: START ::  Handler: Command Line Install
2012-03-09    19:31:43:140    5028    124c    Handler    :::::::::
2012-03-09    19:31:43:140    5028    124c    Handler      : Updates to install = 1
2012-03-09    19:31:43:140    1020    1348    Shutdwn    InstallAtShutdown got install progress.
2012-03-09    19:31:44:793    5028    124c    Handler      : WARNING: Command line install completed. Return code = 0x00009c48, Result = Failed, Reboot required = false
2012-03-09    19:31:44:793    1020    1348    AU    >>##  RESUMED  ## AU: Installing update [UpdateId = {C6CA5181-DDA8-4506-8DE2-40957F118C8C}]
2012-03-09    19:31:44:793    5028    124c    Handler      : WARNING: Exit code = 0x8024200B
2012-03-09    19:31:44:793    1020    1348    AU      # WARNING: Install failed, error = 0x80070643 / 0x00009C48
2012-03-09    19:31:44:793    5028    124c    Handler    :::::::::
2012-03-09    19:31:44:793    1020    1348    Shutdwn    InstallAtShutdown got install progress.
2012-03-09    19:31:44:793    5028    124c    Handler    ::  END  ::  Handler: Command Line Install
2012-03-09    19:31:44:793    5028    124c    Handler    :::::::::::::
2012-03-09    19:31:44:918    1020    129c    Report    REPORT EVENT: {90853F67-1ED4-4EB0-B84C-035CEC83B73D}    2012-03-09 19:31:44:793-0500    1    198    101    {C6CA5181-DDA8-4506-8DE2-40957F118C8C}    101    80070643    AutomaticUpdates    Failure    Content Install    Installation Failure: Windows failed to install the following update with error 0x80070643: Windows Internet Explorer 9 for Windows 7 for x64-based Systems.
2012-03-09    19:31:44:981    1020    129c    Report    CWERReporter::HandleEvents - WER report upload completed with status 0x8
2012-03-09    19:31:44:981    1020    129c    Report    WER Report sent: 7.5.7601.17514 0x80070643 C6CA5181-DDA8-4506-8DE2-40957F118C8C Install 101 Unmanaged
2012-03-09    19:31:44:981    1020    129c    Report    CWERReporter finishing event handling. (00000000)
2012-03-09    19:31:45:012    1020    129c    Agent    *********
2012-03-09    19:31:45:012    1020    129c    Agent    **  END  **  Agent: Installing updates [CallerId = AutomaticUpdates]
2012-03-09    19:31:45:012    1020    129c    Agent    *************
2012-03-09    19:31:45:012    1020    1348    AU    Install call completed.
2012-03-09    19:31:45:012    1020    1348    AU      # WARNING: Install call completed, reboot required = No, error = 0x00000000
2012-03-09    19:31:45:012    1020    1348    AU    #########
2012-03-09    19:31:45:012    1020    1348    AU    ##  END  ##  AU: Installing updates [CallId = {09072B62-42B6-43E5-9319-ABEC0F05A2B6}]
2012-03-09    19:31:45:012    1020    1348    AU    #############
2012-03-09    19:31:45:012    1020    1348    Shutdwn    InstallAtShutdown got install progress.
2012-03-09    19:31:45:012    1020    1348    AU    Install complete for all calls, reboot NOT needed
2012-03-09    19:31:45:012    1020    1348    AU    Successfully wrote event for AU health state:0
2012-03-09    19:31:45:012    1020    1348    AU    AU initiates service shutdown
2012-03-09    19:31:45:012    1020    1348    AU    InstallAtShutdown completed.
2012-03-09    19:31:45:012    1020    1348    AU    Successfully wrote event for AU health state:0
2012-03-09    19:31:45:012    1020    1348    AU    Successfully wrote event for AU health state:0
2012-03-09    19:31:46:541    1020    758    AU    ###########  AU: Uninitializing Automatic Updates  ###########
2012-03-09    19:31:46:541    1020    758    Report    CWERReporter finishing event handling. (00000000)
2012-03-09    19:31:46:743    1020    758    Service    *********
2012-03-09    19:31:46:743    1020    758    Service    **  END  **  Service: Service exit [Exit code = 0x240001]
2012-03-09    19:31:46:743    1020    758    Service    *************

the 31bf... must be windowsupdate in general
 
In any case, I now have the msu for KB2647516, but I have no idea where to get the amd64_microsoft-windows-ie-winsockautodialstub, etc.  Microsoft download center doesn't have those listed.  I found a website that has the unpacked dlls available for download, but I don't know how to install them to tell the windows update package installer to see that I've got them.  I was unable to find at all amd64_microsoft-windows-ie-versioninfo_31bf3856ad364e35_9.4.8112.20546_none_743d1bd020c737d9
 
would anyone happen to have the top 4 from an archive file install.wim on their win7 DVD/CD?  I can't browse my recovery partition and a DOS-based search only finds boot.wim, base.wim and winre.wim, none of which can I navigate to in windows explorer, even if given the explicit path
 

Should this happen to anyone else
 
Download (save to disk) System Update Readiness Tool appropriate for your flavor of OS.
Run it.  Note that on my system with corruptions it took about 45 minutes to run, all the while displaying 0% (stalled) progress.  If you have concerns if it is running, go to taskmanager and see that it updates the memory or CPU usage stamp at least once every 2 minutes.
Check %SYSTEMROOT%\Logs\CBS\CheckSUR.log to see if it wasn't able to auto-repair any issues because it doesn't have the zipped archive (msu).  If there are any, download the relevant package on the Microsoft Download Center by using the search feature (note that 64 bit links are sometimes different than 32 bit links)
Create a directory at C:\Windows\CheckSur\packages
Copy the downloaded msu files there
Re-run System Update Readiness Tool - aren't you glad you downloaded it?
 
 
For good measure I then did
net stop wuauserv
then navigated to C:\Windows\SoftwareDistribution and deleted the contents of the download folder as well as "C:\Windows\SoftwareDistribution\DataStore\DataStore.edb"
(note, this erases your update history)
net start wuauserv
 
reboot
re-run windows update.

edredon

Re:Windows/MS Update prompts me to install an app that already is installed Friday, March 09, 2012 12:45 PM ()

Did you try yet?  There's a Fix it button or you can do it yourself. 

Let me fix it myself 
To uninstall Internet Explorer 9, follow these steps:  

1. Log on to the computer as an Administrator or with an account that has administrative rights.
2. Close all Internet Explorer browser windows.
3. Click Start, type cmd in the Search box and then click cmd.exe from the programs list.
4. Copy the following command and then right-click inside the command window, click Paste, and then press Enter on the keyboard.  
   
   FORFILES /P %WINDIR%\servicing\Packages /M Microsoft-Windows-InternetExplorer-*9.*.mum /c "cmd /c echo Uninstalling package @fname && start /w pkgmgr /up:@fname /norestart"
5. Restart the computer to complete the uninstall of Internet Explorer 9. 
   
   Note: When you uninstall Internet Explorer 9, the previously installed version of Internet Explorer is installed. If the previous version of Internet Explorer is not Internet Explorer 8, you can install and then configure Internet Explorer 8 from the following Microsoft website: 

I just wanted to tell you THAAAANKS!!!
I had to register on EVGA to make sure I marked your answer has a major relief and help others get here!

I don't know where you found this solution but it fixed my 10hours intensive search for a solution on Windows Update errors number: 80092004 and/or 800F081E!

Mille fois merci!

Glad to hear it helped. Welcome to EVGA's forum!