Exchange 2010 introduced that ability to provide a user an archive mailbox however this was only available in Outlook 2010 or OWA.  Microsoft later made an announcement to back port this feature into Outlook 2007 do to customer demand.

Wait no longer, the December Outlook updates provide archive mailbox support for Outlook 2007 and more information can be found here

At 3pm today Microsoft released a post on the Exchange team blog providing more information.