Hi Kitty, after you have found out the interface of the board or even just the model of the motherboard post back and I'll give you some links for the best cards in the price range for gaming. I play games myself btw. You can find out the details of his computer by downloading this program which is free and will tell you everything you need to know:
http://www.download.com/Everest-Ultimate-Editi on-2006/3000-2086-10499291.html
Just download, install, run the program, and select "motherboard" and then "motheboard ID". This is the model of the board, tell me this and I'll advise you on the best card for the money.