I guess it's not a computer made for gaming then but even if you get the game running you will eventually wanna add mods and push the graphics a bit so a tip from me is to take a look at a "real" graphics card. Just bought myself a new ATI HD 6870 (double fan) for 1600 swedish kr and thats about 234 dollars so not really expensive and you dont need as powerful card as that.
But hope you get it running on your computer as it is right now. To good game to miss. Good luck
