Get a Radeon card. This game is heavy DirectX. GeForce's handle OpenGL games like Doom 3 better IMO. I had a BFG GeForce 6800 GT w/ 256 DDR and had nothing but problems running this game. I switched to an ATI Radeon X800 Pro w/256 DDR and guess what? No more problems!
Runs like a breeze on my nvidia 5900XT In saying that, it also runs fine on my wifes ati 9600. As long as the card supports DX9 I don't think it matters other than the amount of onboard ram it has.
to the poster who has the BFG 6800gt. I got the exact same card as yours and EQ2 runs smoothly. It's not the grx card's problem. any decent gfx card should do fine. the problem maybe your other PC setting.