There are PCI version of the Radeon 9000/9100/9200 and the FX5200/5600. They are all neck and neck. Yes the 5600 and 5200 perform about the same, with the 5200 winning more than half the time between those two. Also the R9200 keeps pace as well.
All of them would be better than your current configuration, but it really depends on what you expect. You'd be better off getting a new MOBO with good onboard graphics really. Either the nV nForce2 or ATI R9100IGP would be a good choice that gives you a future, doesn't simply put a band-aide on your old solution. You should be able to get mobo and CPU for near the price of a new PCI graphics card, and the performance diff. wouldn't be much at all in that case, but definitely better than your old board.
- You need a licence to buy a gun, but they'll sell anyone a stamp <i>(or internet account)</i> ! - <font color=green>RED </font color=green> <font color=red> GREEN</font color=red> GA to SK
I could be mistaken, maybe someone can back me up or correct what I say...
I think that there might not be a point to upgrade your card because the rest of your system would be too great of a bottleneck to actually make a difference. If your looking to play modern games, then with the exception of a few older Q3 engine games (MoH:AA, JK2, SOF2) your CPU will drag down your GPU and therefore there would be no point to upgrade.
Write back and tell us why you want to upgrade and then maybe we could recommend something more appropriate.