My son's pc used to have an ATI card (I forget which one) & it was nothing but trouble, even with driver updates most graphic intensive programs refused to play nicely so I switched it for an nVidia card & the problems went away.

Now I'm not saying the nVidia cards are all better than ATI cards because I've only experienced one ATI & some of the driver updates for the nVidia cards have caused problems in the past, but I personally would go for nVidia every time, partly due to that one experience & partly due to nVidia fixing the problem drivers in pretty short time.

Windows 7 64Bit
Poser Pro 2010 SR1