Mark Lyon's GMail Loader (GML) - Import Your Mail into GMail
"Some of the benefits of GMail are the large storage space, easy labeling of messages (instead of sorting into folders), and quick Google-powered searching. As an email packrat, I jumped at the opportunity to have all my email easily searchable. I decided I would import all my old email from Netscape Communicator 4.7 (which had messages in it dating back to 1994). There was no upload feature included with GMail, however.
So I wrote one."