Upgrade Graphics cars or CPU?

are you looking for a gaming upgrade or an over all computing upgrade?

if gaming i would go with a new gpu perhaps a 5770, or 6950 depending on your budget.

if your wanting better over computer performance a new cpu would be a good decision. If you want better computing let us know what motherboard you have and we can select the best bang for your buck.

depends on what resolution you are trying to play your games at
if your maximum resolution is 1600 x 1200, getting a new video card is useless but if you want a DX11 card, go for the Nvidia 4 series (460 and up)
you have to make sure your CPU is Dual Core or Core 2 Duo
Upgrading to a Quad Core is not a big jump from a Core 2 Duo
but getting an i5 or i7 is worth it
If I had that system of yours I'll wait for a year at least, because you can run all the games on good settings even crysis 2