If you're upgrading to a high end GPU you'll need to upgrade that CPU to maybe a Core 2 Quad, which are cheap nowadays.
You didn't read the topic, did you?
Also, a suggestion for your video card:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102918I've noticed that you run at a low resolution, to take max advantage of your GPU you would have to upgrade to a bigger monitor, one that supports about 1920x1080 resolution.
I would help you further, as I can see that nobody else is, but as Righteous One pointed out, I'm not that knowledgeable in the building area.