Digital Grabber has posted a guide to reinstalling Windows XP

If you have been running Windows XP for a couple of years or more you may find that it is not running quite as quickly and smoothly as it was when you did your first install. I am constantly 'evaluating' software and uninstalling and reinstalling beta software on my computer and have always gradually become more and more disappointed after nine months to a year with the performance of my PC. So I regularly do a backup and reinstall all my software, including Windows. This is the step-by-step.

Guide To Reinstalling Windows XP