Kes! I am having the same problems with my GF3 Ti200. It will work with flight sims, but games like Ghost Recon, Op Flashpoint it just craps out.
I have been trying now for over a week to sort this problem out.
I was told it was a power supply problem (was using a 250w PSU, which ran it ok for a year!) so bought a 350w PSU (and it seems to be a decent make). Still does it.
I have tried everything from drivers, to conflicts to voodoo! But nothing is working.
It is baffling that it will work with some games and not others!!!
I did try my old Prophet 4000XT (32Mb) back in and it did run these games, so I thought it was a PSU problem but as I say I replaced it......and I am only running a Duron 850, a sound card, 40G HD and a CD-Rom drive - hardly taxing.
So, I am at an impasse, and it the same boat as you....