Legion Hardware checks out whether it's possible to give a somewhat older system a nice performance boost with a budget AGP graphics card:
Those currently using an LGA775 or 939-pin AGP system are most likely better off purchasing a new motherboard and graphics combo that supports PCI Express rather than buy a new AGP card. However, this option is not for everyone and most gamers will be happy if they can get some more quality gaming action out of their system for a little over $100 US. Unfortunately, I do not have a Socket 754 or 478 system on hand that supports AGP 8x graphics cards. Therefore, I have installed the HIS X1600Pro IceQ AGP 256MB graphics card in an Athlon64 939-pin system.