I've just installed ccleaner and it's removed about 100MB of unnecessary 'stuff'. Hopefully none of the things it removed are vital to the health and well being of the system.
Normally I'm a linux user but need to run XP on my laptop as a newly purchased CAD package only works on XP/Vista. My Windows skill level <= newbie
I also took the opportunity to install AVG and SpyBot - on the recommendation of someone who knows what they're talking about.