What operating system?
Ccleaner seems to be pretty good, it's not too aggresive so less likely to remove something you need.
Just leave it all on the default settings. Available directly from www.piriform.com and various free download sites, also often on the cd/dvd's that come with computer magazines.
Another fairly safe option is windows live one care, also free-
http://www.microsoft.com/uk/athome/security/update/windows_live_safety_center.mspx
As always, back up all your data to cd/memory stick, and create a restore point ( if your operating system supports this) so you can get back to where you started if it all goes wrong.
spud, January 2010
