OMG, you bought Vista?! Change this shit to Windows 7 (you have got 4GB RAM, WinXP may have problems with reading all of that space), because it's slowing down ALL games. Then reduce details one step down (if you loaded "PC of 2009" set, load "PC of 2008")
If it didn't help, you should buy new CPU (I know that is expensive).
I don't know anything about this graphic card, it also can cause problems.