I use the 64 bit with a 8800gts 640mb factory o.c. and when I play certain games like hl2 deatmatch I get horizontal distortion lines across the whole screen. Some games I get nuthin. Is this a bad card or vista or perhaps the games themselves.
What version of the driver? The current 'official' WHQL driver (version 100.65) has a lot of known problems. It might be certified by Microsoft, but that doesn't mean it's feature-complete. It only means that Microsoft doesn't think it'll crash your system.
There's a newer Beta driver (101.45) that fixes a lot of gaming problems.
That said, the 101.45 causes *tons* of blue screens of death for me when watching xvid videos.