exporting old email out of outlook?

I have a somewhat knotty problem I'd like some help with. When I was young and naive (1997 or so) I set up Microsoft Exchange for my email program. Since I wanted to keep all my old email, I've been stuck with Exchange (or, for the last 4 years or so, Outlook) as my email client ever since. Is there any decent way to convert all of those old emails (this would be thousands upon thousands, I've been online for years and don't delete old email) into some form such as .txt files so I can get rid of Outlook and move to a linux box? It's about time for a new computer, and I'm sure as heck not getting XP. I'd really prefer not to lose all of my old email, since some of it has sentimental value. Outlook seems to store it as one big icky file. Any suggestions?