Graphics card and RAM are the two components to upgrade when you're looking to play games. I checked the specs on your computer - you have a PCI Express x16 slot, which means you can use any of the most recent graphics cards in this particular system. You also may want to pick up some DDR2 RAM to upgrade the memory. And depending on which graphics card you upgrade to, you may also need a new power supply as well. Most Best Buy stores carry all of those components, so head to the store (you can bring your computer with you if you'd like Geek Squad to install the parts for you) and ask a Geek Squad Agent for advice on what to do with your computer.