Actually, Microsoft has Outlook 2003 Personal Folders Backup, an Add-in program that will back up your PST file at regular intervals. It integrates directly into Outlook itself. You can back up your PST file to a separate drive and location, like an external drive. You can also set how often it backs up. This works well for me. Here is the link.
http://www.microsoft.com/downloads/d...displaylang=en
Hope this helps someone.