simple answer is the easy route, archive your emails to a file on the pst folder, once this has been done you will have no emails in the box, then goto file, and open data file and point to the folder and pst file, this will open up the file and add it to your outlook bar as a second folder.
goto tools and options and change the mail options to start from your new added folder.
this will then use the created PST file as primary.
you will not be able to roam after this if you change machines unles your folder is in your roaming profile.
hope this helps