Game lagging and then a strip of artifacts

[gendriks]

I'm playing on a GeForce 6800 on WinXP, and sometimes the game will lag out for several seconds, and then come back with a strip about 3/4 down the monitor not rendering properly. The only way i can describe it is if you used the noclipping cheat in Doom and ran out the map, and then looked back onto the map. It's kind of like that. The rest of the screen is fine though.

Should I be forcing DX or oGL rendering to fix this?

What should I do?