What version of outlook? There are a couple of different options. You could archive everything up to today which creates an archive folder here:
C:\Documents and Settings\username\Local Settings\Application Data\Microsoft\Outlook
You will need to ensure all files and folders are visible to see this.
You could also go to File–import and export–export to a file – choose file type desired (.pst is easiest to import back I believe) and do what follows.