I'm surprised that your Video Card isn't bottle necked from your CPU
I mean running a low end CPU with a high end video card in not advised
you can at least get a Core 2 Duo, you will feel lots of difference
the 8800 GTS is a beast and need a good CPU to handle it
Intel Core 2 Duo E7500: 140$
http://www.newegg.com/Product/Produc...82E16819115056
I hope that you have a good quality PSU as well