1stly the graphic card manufacturer doesnt have 2 be anything like tha manufacturer of the motherboard 2 work any pci-e card will work in a pci-e slot same with agp cards and slots.
2ndly A GeForce 7800 would do da trick

but theyr xpensive, agp graphic cards are more costly and u get a lot less performance out of ur card.
At the moment i have an agpx8 motherboard and considered byin a agpx8 graphic card but i found that it would be cheaper 2 buy a new pci-e motherboard 4 £70 and buy a GeForce 7600gt 4 £130 (the 7800 is £180 and its slower than the pci-e 7600)

the main drawback with agpx8 cards is that the clock speed is decent but the memory speed is halved because of the slow graphic port. If u upgraded 2 pci-e u wouldnt have 2 upgrade ur pc motherboard wise 4 a while u can buy faster graphic cards 4 a smaler price.
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Hope this info helps you choose a gd graphic card.

(u dnt have to buy a 7600gt its up 2 u)