It's about time...
The Office 2007 Cumulative Update for December 2010 finally includes Exchange 2010 archive support, as well as a bunch of bug fixes. Strangely, the website for the update doesn't list anything about this support.
Take a look at the article, "Yes Virginia, there is Exchange 2010 archive support in Outlook 2007" on the Exchange Team's blog for details about Exchange 2010 archive support. The site also explains what Exchange archiving is and how it works with Outlook 2007.
With the release of this update, organizations with Office 2007/Outlook 2007 deployed can benefit from Exchange 2010's archiving and retention features.