If you want to free your computer of useless system files, try CleanCache 3.3
. This free program removes Windows' temporary files, Office's most recently used history, and browser cache files. You can either run a complete Cleanup or just clean a set of Checked Items. One problem with this is that although Clean Cache has the setting to preserve useful cookies; but even with this option on, you will have to click 'Remember my address and password' again on many of the sites you visit regularly. So it is better not to clean your cookies using this software if you don't want to enter your password again anad again.
To install this sofwtare you will require to have Microsoft's .Net Framework, which you might have already got or you can get it at www.microsoft.com.