Look at my post above. A 3.2 ghz processor will cost you £20 less with AMD than Intel, so no Intel arent cheaper. As for just shoving another processor in there. Celeron processors are socket 478. This means only celerons will fit in it. And I am afraid to say that you have the fastest celeron that can be bought. No matter wether you go for AMD or Intel, you will need a new motherboard. If price is your issue, then AMD will save you quite a bit, however if you want intel, and have the money, go for it, neither Intel or AMD will be noticably better than the other at anything, just in benchmarks it will show up a bit.
