if you are using an HP computer you are going to need to upgrade the PSU as well as it will not be sufficient for any decent card.
Here are his specs
As far as recs go, Id replace his power supply with this
and grab this graphic card
Considering both have rebates and the GPU is a very solid card that comes with Bioshock Infinite and the newest Tomb Raider game that he can either play or resell thats a really solid deal.