I can't think of many graphics cards that are PCIE x4 - the standard for modern ones is PCIE x16.
Looking up your model, it seems that you do have a PCIE x16 slot and and AGP slot. You could select many newer model graphics cards, as long as you have enough power.
You might run into a bottleneck with your CPU, etc, but it all depends on what you want to do with it anyway.
What's your main purpose for the computer?