Seeing that Outlook allows for automatic and manual archiving, it only makes sense that it can also open an archive file.  To do so, select File, then Open, then Open Outlook Data File.

In the Open Outlook Data File window (which defaults to the My Documents\Outlook Files folder), select the data file you wish to open (archive in this case) and click OK.

The above window will close and you will be back at your Outlook Home screen.  To view the archive folder, scroll to the bottom of the folder view (left side), double-click Archives to expand, then double-click Inbox to expand, then select the folder you wish to view.  The archived email will then be displayed.