I would reccomend going to http://www.systemrequirementslab.com/referrer/srtest and choosing the game you wish to play from the drop down (It will require installing a 1-off plugin)

And the reccomended Graphics card is a 7800 GTX - So a low end card, but I would reccomend you have something in the Nvidia GeForce 8/9 Series, and Nvidia not ATi