With an upgrade to your graphics card you could probably run med-high settings on low res. Your processor will bottleneck the better cards around, however. So a modest upgrade will get you running the game. Say geforce 9800?
Technically, I'd advise you to update your motherboards BIOS through asus's Website. Grab a good Video card, if your PSU will support it. Then, you can also try to go the route of slightly overclocking your CPU a little. Any little bit will improve your performance.
That would take a little bit of research if you're not too computer savvy.