I wouldn't go for a NVidia card, especially if your running Vista and/or you are using AGP...
I simply can't play almost all my games using a 7600GS AGP on Vista, and it worked perfectly on XP...
My ATI 9600SE was allways great though, if a little slower, but definitely more stable and the drivers were better.
People *allways* tell me Nvidia is better, but I've never actually experienced them being better myself...!
Alex. :-D