Next to the fan speed, see the button that says auto? Click that and the orange lights at the top and bottom of that button will turn off. It will then let you mess with the slider. Caution though, if it is already running at 100% then there is a reason for it. Keep an eye on your temps, I would worry with anything over 60c idle and over 86c in games. Remember, if you lower your fan speed, it will not adjust if it gets higher, running the risk of shutting down your GPU (and your PC with it).

What is the model # of your 9800GT?

9800GT SC, P/N 512-P3 N976-AB
 
It has 2 DVIs, no HDMI.

You know, now that you mention it, I think that it may be "-AR" at the end, not -AB".  It was still in the case, and I read it with a flashlight, the first time.  I just looked again, and now it does look like "-AR".  I checked the link that you sent, and yes, the card appears to be the same.
 
I do have the latest Precision installed.  I was also unable to adjust the fan speed in RivaTuner, but I think that I may not have had all of the functionality, as it said that my drivers were not in its database (they are the newest NVIDIA drivers).
 
I just received the card, from me brother-in-law, who was using it in an SLI configuration until he bought better cards.  He bought it about 2 years ago, I think.  I actually have another (ATI) fan-less card, but it has this huge heatsink on the back of the card, which prevents me from putting it in PCI-e slot 1, which on this motherboard (XFX 780i) is required for non-SLI operation.  That card would work fine (and quietly) in PCI-e slot 2 or 3.  So, that's annoying.
 
I will check to see if the EVGA card has 2 or 3 wires for the fan, although in theory, a 2-wire fan can be adjusted; it just cannot be monitored (I believe that the 3rd wire is to determine the speed in RPM of the fan).
 
Were there any BIOS changes for this card?  I could not find any.  I thought that maybe a newer BIOS version might help.   Video BIOS version on this card is "07/16/08".
 
I may just end up connecting the fan to one of the motherboard's fan connectors and adjusting the speed from there, in the motherboard's BIOS.  I don't really play games on my computer, so it shouldn't get very hot.  Like I said earlier, it was hovering around 46'C, which is quite cool.