All I do is:

Weekly virus scan with CA Antivirus
Weekly defrag
Daily Ad-Aware by Lavasoft
CC Cleaner a couple times per week.
Dr. Web's "Cureit"  once or twice a month

I also empty my firewall cache a couple times per week, as well as my browser cache.

I also have "Start Up Manager" which is a free program that allows me to turn off programs running in the background.  I don't know how to access the start up manager in XP Pro, so this little program works well for me.

I also snagged the "Cleanse Uninstall" that was a freebie download at "Giveaway of the day". It allows you to uninstall programs and it searches not only the hard drive but also the registry and removes all files related to that program you are uninstalling, including registry entries.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi