26 Apr 2008 at 23:15 - 45
Buying a PCI-E capable mobo is a lot harder than it sounds, because now you'll have to buy a processor that will fit the socket type (because we know you can't be using the same processor). You probably need new RAM, because, for example, even if you get a socket 939 AMD mobo, you'll have a hard time finding a socket 939 AMD cpu, thus requiring you to go AM2/AM2+ and finally requiring you to acquire DDR2 RAM. New power supply? Yeah those newer boards require a 24pin rail instead of the old 20pin ATX rails. Of course, those are just the some of the conflicts you *might* encounter. So, with all that out of the way, let's take a look at what you can do.
Return the 7900GS PCI-E, buy 7900GS AGP.
I think you were just confused that there were different version of the card.