What video card is great to play games on if I have a mac with Windows XP on it?

I want to play some the games my friends have such as Left 4 Dead and other great games on XP, but my video card is not good. What video card should I get that works with both mac and PC. I want a video card that doesn't make the game run slow.|||listing a price range, specs of the pc, and type of pc would be helpful

I would look into:

Nvidia 9800GTX+

Nvidia 8800GT (if you can still get it)



AMD 4850