Windows XP has a secret "System Profile" folder hidden within Windows folder that can possibly contain Gigabytes (yes, with a G) of data that could be deleted from your hard drive to save space which is ignored by all of the programs that clean up temporary files.

To clean out this directory, you must first enable viewing of hidden files and show the file extensions of recognized files.  To do this, open "My Computer" then click Tools > Folder Options.

Then under the View tab select "Show hidden files and folders, uncheck "Hide exstensions for known file types, and it's a good idea for stability reasons to make sure "Launch folder windows in a seperate process " is selected.

Click OK and then click Start > Run and paste the following path into the run box:

"C:\Windows\System32\CONFIG\systemprofile\Local Settings\Temp"

Then click OK.  This will open the system profile's temporary files folder.

You can safely delete everything in this folder.  If something happens to be in use, skip it and continue deleting.  The older your install of Windows, the more files you will have in that folder.

Happy Hunting!