Never EVER use any of those crap Registry Cleaner programs. Do a basic (but important) clean-up yourself using the steps Entwood posted.
Those 3rd party programs are just another memory resident program which use valuable resources and clogs things up.
However, as already stated, the only way to get the system to work like a 'new' machine (when you first got it) is to Format and have a fresh installation of XP.
I used to format and reinstall Windows on a weekly basis. That was back in the Windows 95 days. Now, I tend to do it every 3 or 4 months.
USB sticks are so cheap, and transfer rates are so quick that there is no need to store your personal stuff on your HDD anymore. Bang it on a Flash Drive and its always with you, or always somewhere 'safe'.
All the Applications I need to install are on a single DVD. Takes about 45 minutes start to finish to format and reinstall everything;
Windows XP SP3
Office 2003 (the only version to use)
Adobe CS2 (Photoshop and Illustrator etc)
Quark 5.0 (again, the only version to use)
Nero 6.6.1.6 (as above)
Other crap I use.
When you get into a routine of Formatting and re-installing, you'll find you actually save time by doing it.
