Since you are using a socket A, you will have either a PCI or AGP slot (your mobo model doesn't exist or you typed it wrong).
You need to make sure that your power supply is up to whatever card you choose, and that you buy a card that will go into whatever slot your mobo has. Here's a pic to help you determine if you have AGP or not:
My wife's computer has an Athlon XP 2000+ and is running a 6600GT. I had to replace the power supply with a 300W as the 6600 requires it, though.
You can check the list here
to see how the cards stack up against one another.