with how old the system is...I don't think that he would have a PCI-E slot...

edit: quadraxas got the answer before me

The best thing to do would be to build a new one, allstarshop.com has great prices, but if you don't feel comfortable building a pc I could help you get something in your price range, just pm me if you wish. I could get you a good pc from $500 to $1000 depending on how good of a system you want, and allstarshop has optional installation and windows install for a small price. They also have warranties for everything you get, and you have a 1 year return policy in case something doesn't work.

If you don't want to build it completely from scratch then check cyberpowerpc.com, they have some cheap but good gaming pcs, although you could build something better for cheaper.