If you're using the integrated graphics processor that came with the machine then that's probably where you need to spend your money. The integrated stuff is always way underpowered.
A decent PCI-E video card will make a huge difference in your gaming performance. Tom's Hardware has a really nice chart to show the relative performance of current cards (
http://www.tomshardware.com/charts/d...%2C1565%2C1605). Look at that chart then compare sites like Newegg and Fry's with what's in your wallet to decide what works for you. I would consider the cards comparable to the Nvidia 7800 to be a good starting point. Go up from there according to your budget.
Tony