also I know nothing about ATI cards, do those support shader model 3 or 4?
Two of them explicitly state the answer to that question in the pages I link to. The first one, which doesn't, is SM 4.0.
Actually, its a gateway, and it has 1 onboard AGP, and 3 onboard PCI (non-express)
I think you misunderstood me. Onboard AGP would mean that the videocard is built into the mainboard, and you could not plug an AGP card into it. Your reply suggests that you actually have an AGP slot, in which case, why buy a PCI card when you have an AGP slot? You most certainly can get an 8800GT in AGP form.