First of all...I am in NO WAY a computer expert. I'm just on it waaaaay to much. I don't know anything about programming, or any of the behind the scenes stuff. So just be warned that when tweaking your computer, you should keep track of what you change in case you need to change it back.
Having said that, I found a really great website for PCs. The link I'm going to send you is to a thread that is about tweaking XP in for faster and better performance. Again, TWEAK AT YOUR OWN RISK. Most of the long time members at the site seem really knowledgable and professional...but you just never know.
Cyber Tech Help
Hope this helps!