Its not intensive at all. I have a 2.1ghz AMD dual core and a HD3850 and i get a solid 60fps everywhere at 1440x900.
Your video card is not up to spec anymore. It hasn't been for a while now. Games are getting to be more and more graphics card intensive, and a 7600GS (not even the GT mind you) is not capable of keeping up, especially at whatever resolution you are trying to use it at.
In most comparisons, a stock 7600GS preforms about the same as a 6600GT, which is the minimum for the game.