I know it may seem stupid to use this version but I'm a 'c' developer and I'm pretty sure that the problem comes from the drivers(otherwise I swear I wouldn't be here cause I've suspected everything else before this).
Of course I can't confirm this because I don't have access to the NVidia's source code (unfortunately) .
I'm using the exact same binaries on another computer that uses another video card
(3dfx Voodoo) and everything works great!
Of course it may be a X problem but I've tested a lot believe me!
I'll give it a try just to make sure but maybe someone knows about it so I'll wait a couple of days just in case I wouldn't have to reinstall X.