Yea, find your PC on there using the useful tool they have. If it's that bad Axel then you really need to upgrade it. Also, just because it's 3.0 GHz doesn't mean it's up to par, my CPU's clock speed is only 1.8GHz and I run virtually lag free.
I think it depends on the motherboard/case model. The most common standard is ATX. Find out what standard your case/mobo is then find a compatible PSU for it.
Your running other things in the background right? Ventrilo? MSN? any other unneeded process. They're all going to use up your hardware, best way to fix that would be to update it.
