Alright, well, windows is easy enough.
Find files/folders: Search for *.tmp, TEMP. Delete em.
Since youre using windows 2000 prof. I assume youre using Internet Explorer. So, on the subject of Temporary internet files. Delete everything but the folder itself, if you have windows explorer available, itll show you all the files rather than just a finite number of jpgs, gifs, and cookies. Delete them all, despite the warnings about things not functioning properly. Microsoft just sucks. Delete all your cookies too, you wont be needing those anymore.
If you can download programs onto this computer, I strongly suggest AdAware, available at
http://www.lavasoftusa.com/
Get the RefUpdate too, so that you can find even the most recent spyware/hidden cookies and such.
Beyond that, my only other suggestion is to format the harddrive, reinstall the OS, the business package, and all the drivers for mouse and keyboard and printer and network and such. That however is time consuming, I guess it all depends on just how clean you want this drive.