id say avoid tablet pcs for autocad but if he must have one
 
the HP touchsmart tm2
 
it can be given a ati 5830 i think or something like that
 
and its convertible which adds to the ability to type if needed

I've never heard of using a tablet for AutoCAD.  Even when I was working as a mechanical drafter, none of the senior people used a tablet.  We all had dual screens but that was it.  I don't see how using a tablet would be efficient either as a lot of what you're doing is entering shorthand commands and numbers/words.
 
There are apparently people who use them - I suggest Googling it as I did.  There have been posts with people using the Calcomp 12 and others.

I have a Tablet with AutoCAD 2009 and Inventor on it but only for when I am on the road.  I do all my main design on my work station though.  Don't go with a tablet.  If you want to go mobile, try to go with something that has Quadro graphics or FireGL.  Also make sure you have plenty of memory on the graphics.  Intel Core series chip with at least 4gb of memory (Go for 8gb if they have the money IMHO).

when your talking about 3d graphics (im a Skills Usa 3d animation silver medalist =P ) i HIGHLY advise for any mobility go with a must plug in laptop
 
ie alienware or sager (which i say sager is best)
 
hell be able to plug it in and run it anywhere
 
BUT the battery wont last longer then 30 mins maybe XD
 
http://www.sagernotebook...index.php?page=products
 
workstations more specifically as they use quadro
 
not the greatest for gaming but very stable which you want

AutoCAD is a program by AutoDesk, it is a drafting program that lets you design things, not like paintbrush or photoshop, its more technical with scalings, rendering, dimensions and such.  Its the kind of program used to design a building, car or cellphone casing. 
 
That said, are we talking about a Tablet PC with a touchscreen and no keyboard, or the normal large pad-like accessory used with CAD programs as an input device, called a tablet?  These are two different things entirely.
 
If we're talking about a PC, then go for a midrange laptop with a 64-bit OS and lots of RAM, assuming he/she has a student version.  But, if your friend has a professional licence of at least a year, then the laptop must have an AMD FireStream or Nvidia Quadro card whichever is supported, and not a Radeon or GeForce counterpart.  While game cards can take care of over 90% of the job of a professional card, the latter takes it to 100%.  So it will depend on your friend's needs for reliability and precision.
 
I have installed another CAD program on my new 13.3" Toshiba Satellite L635 laptop that uses the iGPU in the clarkdake CPU, its more than enough for 3-view drawings or simply stuff.  But, if I needed rendering with photo like quality, that's the point for better dedicated graphics.