This tutorial will show you how to find Microsoft's Really Hidden Files, and thus allow you to find out what web sites people have been visiting with Internet Explorer. I say visiting with IE because if you use a decent browser like Firefox you won't have every single thing you look at permanently recorded.
It is actually a very easy process. First you may want to open another (IE) browser window. Now you can paste the following into the address bar:
%userprofile%\Local Settings\Temporary Internet Files\content.ie5\
In that folder, Content.IE5, you should have about 8 folders with names like BO4QGSSI. In these folders should be every site you've ever gone to. The pics, videos, and everything else is all saved as well.
Microsoft uses the desktop.ini to make these folder super hidden. If you delete the desktop.ini Windows will autocreate it the next time you reboot, but if you just edit out the part that makes it work Windows will be tricked into thinking everything is OK. Even if you turn on show hidden files these stay hidden. If you clear out your internet cache these files stay. This is both a security risk and a waste of harddrive space. The only ways to get rid of them are to format, or hack Windows. I have made a batch file that should help you with making these unhidden, as well as discuss more in depth as to what is in these files. It is here.
For further info on hacking Windows, or why this was done try searching, Microsoft's Really Hidden Files.