Im in work at the moment, but I've been playing FF7 for the last month on my Nvidia GF 8800 GTX without any problems, I've got the saint's patch and some others installed but it all runs fine for me, and I've got a dual boot Vista/XP and it works on both.
As soon as i get back from work i'll post up my details, drivers, patches, settings etc etc and see if we can get it going for you...
FF7's fine.......it's FF8 that's shafting me.
[Edit: I just booted into my XP partition only to have it blue screen, cough, fall over and die. Im gonna re-install my XP part and start from scratch again, soz for delay!]