AGP is better than PCI because AGP is faster than PCI slot. But, as you all have said, PCI-Express is a lot faster than AGP and they are going to take over AGP.

If you're planning to buy a graphics card, look out which one that suits your motherboard and not the newest ones will work. OK, seems like you have an AGP slot, I suggest that you may buy an AGP graphics card. Watch out for AGP 4x and AGP 8x too, AGP 8x cards will have its performance decreased if you plug it into 4x slot.