OK, see what you mean but generally that is down to the architecture of the motherboard and doesn't really apply to the processor as you could fit the exact same processor in a different board and it would still cause you problems (I would bet that your processor is fine BTW). XP is pretty good at picking up these changes but I would just go the extra and buy a hard drive brand new for £30 - £60 and do a fresh install and pop the old drive in as a slave. You will need to re-install your programs but the files that matter will be fine.
Five years ago stuff was relatively expensive, I just built a dual core pc for my sister that goes like stink, will run any game or application for the next two years for £380 + VAT. Same as you used to do, board, processor, memory, power supply, graphics card case. Jobs done If you want the specs let me know.
BTW, I am no expert and don't do machine building for a living. I may just be talking shiiite