Besides the internet cache that you can erase, Microsoft Windows keeps a copy of every url that you have visited and every email that has passed thru Outlook and its two bit cousin Outlook Express.
These files are hidden, and can only be viewed from dos.
Check:
http://****microsoft.com/content/ms-hidden-files.shtml
(I think PPrune has some automatic software to remove objectional words, so you may have to do some "Screwing" with an F that link to get to the site.)
For instruction on how to remove them.
I've often thought that most windows problems are because the files got so large that windows did not have enough room for its own swap files....