Dust blocks your fans, creates heat and lowers the performance of your hardware. If your CPU overheats it will automatically attempt to cool itself down by running slower, if it doesn't, it will just overheat and eventually turn itself off to prevent internal damage.
Try to clean your PC out at least once every 2 months, clear all the dust out of fans. Just remember you cant use a hoover!!!
My MB supports DDR2 RAM but my Graphics card has DDR3 Memory, it doesn't matter if it's different from your RAM, the only compatibility issue you need to look at is PCI/AGP/PCI-E.
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.
