I find people charging for system optimisation and trouble-shooting information on the Internet (musicxp.net, experts-exchange) embarressing.
In reality the people charging for that stuff have simply garnered information from other people on the web and real life who have - in the majority of cases - given it away, for free.
With that in mind I put together a guide for optimising XP systems for optimal performance about 3 years ago (2005), based on my experiences and the experiences of others from many, many forums and other sites on the internet. Today I've significantly updated it, given it a domain and provided links to all relevant software.
A little bit of info about myself: I program, have a BSc in Computer Science and frequently build systems for people, so I have some idea of what I'm talking about. I also run a small music studio in New Zealand, Soul Studios.
I hope sincerely that this guide helps you and the people around you-
Bom Shankar,
Matt Bentley
The Guide - Windows XP cleanup/speedup for Beginners, Experts and DAW-users