Sc2 not running smoothly for me, suggestions?

Okay, its most likely disabled already. For kicks, you can update your Realtek audio driver found here (if you got THESE up-to-date with this months or even the last few months release, I'll be impressed).

As for CPU support, your pretty screwed, only P4's. At least you have plenty of affordable video upgrade options.

 

Would buying a new gfx card fix my problem? Or I have to get a brand new pc.

 

Its difficult to say BUT....

You should get a new GFX card first. PCIe 16x is still the standard. IF that didn't do it, THEN you could replace your machine and swap in the video card you just bought. So its not like you really lose in the long run either way.

PS (If you get an ultra high end card, you will probably have to upgrade you Power Supply Unit).