Alright well I think you are confused about a few things, AGP is an interface where you can put in video cards, it has been replaced by the newer PCI express interface. Your motherboard is older by the sounds of it so it's probably AGP 4x, maybe 8x but im thinking 4x probably. Since your CPU isnt so hot I dont know how much you will benefit from a great AGP card like a 850xt or a 6800gs, and since y ou say you only have 300$ Id say go with a 6600gt and upgrade your ram to at least 512, preferably 1 gig. If you have 4x you will have limited bandwidth on any fast agp card, probably even on the 6600gt, but it will still be a large step up from your current card.