Got a call from a guy that lost all his mail in Outlook Express, so I thought that I would pass this info on, and perhaps save someone's cry for help, since this link explains on how to backup the mail and your contact list.. it should be done on a regular basis if you have important mail and contact info stored.
http://support.microsoft.com/?kbid=270670
All I can add is, after you copy the files, then you should burn them to a CD, and keep the CD in a safe, dry, greasy free location.