Microsoft has an Outlook plug-in that backs up your pst files into a location that you can define. You can even choose which pst files you want to back up and how often it reminds you.
What it does is offer to make a copy of the pst file to the backup location when you exit Outlook (depending on how often you tell it to remind you). From there, I guess you can burn the copy once in a while onto a CD, or drag it to an external disk.
1GB may take a long time to replicate each time. If you archive the mail in separate pst according to year, only 2005 will be active and need active backing up, saving you time.
The plug-in is backward compatible to OL2000. Find it here