You do not meet eh requirements for that game.
What video card do you have? It must support DX 9c/SM 3.0(X1900 or Geforce 6600 and better for the most part.)
Steam has the requirements listed. You seem to be under even the minimum and even at the minimum you will not get a great game play experience.http://store.steampowered.com/app/34830/
At a minimum you need a faster cpu(or some overclocking) and more memory. Maybe even a new video card.