|Here's a link to your system specs:|
Here's a link to the specs of the motherboard used in your system:
As grasshopper said, it has has standard PCI slots only...no AGP, no PCI-express. There are PCI graphics cards available & just about any one of them will be better than the onboard video, but you'll be limited in which games will be playable. More recent/modern games will most likely NOT be playable, but games that are at least a couple of years old *should* play OK...it would depend on the game. You should also have a fair amount of RAM for gaming. The mboard accepts up to 4GB of DDR2-533. You should have at least 2GB.
Here's a couple of video card possibilities:
GeForce FX 5200 256MB 128-bit DDR PCI Video Card - $30 after rebate w/free shipping
GeForce 8400 GS 512MB 64-bit GDDR2 PCI Video Card - $40 after rebate w/free shipping
I don't think I'd spend any more than that.