*scratches head*

I'd say upgrade the processor. Socket 775LGAs are outdated, I think, but you should be able to pick up something from eBay, I'd imagine.

Probably see about replacing that PSU as well. I'd actually put that on a higher priority than upgrading the CPU.

Still, I'm not very reliable when it comes to hardware. Let's hear what the rest of the lads have to say.

...n00b...

EDIT: Actually, why don't you run PCMark? It might give a better indication of all-round PC performance, as opposed to graphics performance that 3DMark goes for.