You can always 'fix' your CVars in XP too
This site is very detailed for the DIYer, it really takes forever this way
http://www.tweakguides.com/Crysis_1.html
Or you can download this thing which is a CVars already set to go, you'll have to change the brightness, contrast, & gamma to fit your monitor though.
http://www.crymod.com/thread.php?threadid=13790&page=1
As for the card that can run this smoothly, both the 3870x2 & GX2 can @ 1920x1200 or less. The GTS can do it @ 1440x900. The 9600gt just don't have the power, or the shaders, to do it - SLI'd or not. & like DanishDevil said, always backup your CVars.
That CVars make Crysis look & feel better by loading all the textures into a cache instead of updating it every time you move, which can make even the fastest pc's go into permanent hibernation
