You never know when you're going to need an Outlook message that was archived long ago. In a comment on a previous, Cliff Brandt asked how to move a file from the archive to one of his main Outlook folders.
Doing so is a breeze, but keep in mind, an archive relocates only Outlook data of a specific age and is intended primarily to keep your Outlook.pst file a manageable size. A backup copies all your Outlook data and allows you to restore all your messages, contacts, tasks, and calendar entries.
The best way to back up Outlook is to use Microsoft's free Personal Folders Backup, available in versions for Outlook 2007, 2003, and 2002. Microsoft's Help and How-To site provides instructions for backing up Outlook 2003. More information on backing up and restoring .pst files is available on the Microsoft Support site.
Create an Outlook archive
In Outlook 2007, click File > Archive, select the folder you want to archive, and choose a date in the drop-down menu next to "Archive items older than." If you want to store the archive in a location other than Outlook's default folder, click Browse and select the location of your choice. Once you've chosen your archive options, click OK.
Instructions for creating an archive in Outlook 2003 are on the Microsoft Office Online site.
To open an archive in Outlook 2007, click File > Open > Outlook Data File, select the archive file you created previously, and click OK.
The file will appear in Outlook's left pane. Choose the folder containing the message you want to retrieve, and then drag the file from the right pane into the folder of your choice in the left pane.
To enable or disable Outlook 2007's AutoArchive feature, click Tools > Options > Other, choose the AutoArchive button, and check or uncheck "Run AutoArchive every." The AutoArchive dialog box lets you choose how often to archive, the age of the archived entries, and the name and location of the archive file. Make sure "Show archive folder in folder list" is checked before you click OK.
The Microsoft Office Online site lists the steps for auto-archiving folders in Outlook 2003.