Quote Originally Posted by Jay Pace
New processor (which? there are a billion and I haven't got a clue what the difference is)
I'd get an AMD. You get more bang for your buck.

Quote Originally Posted by Jay Pace
New motherboard (does it matter which one?)
The motherboard has to match the kind of processor you're getting. e.g. Socket 939 or whatever.

You can buy packs which come with motherboard and processor.

Asus are quite popular. One of my workmates just got an AS Rock board which was a bit cheaper, but seems fine.

Quote Originally Posted by Jay Pace
New cooling things - Case cooler? Memory cooler? PSU fan?
You will need a fan for the CPU - normally included, a fan for the case, and possibly a fan for the Graphics card. You can often get away with a good heatsink.

Quote Originally Posted by Jay Pace
What are the noisy things in my PC that need to be quietened?
Generally just the fans.

Hard Disks can sometimes be noisy.