How to move WSUS 3.0 to a new server
this article will outline how to migrate WSUS 3.0 to a new server using a local SQL Express instance and without downloading all of the updates again.
http://www.capslockassassin.com/2008/09/22/how-to-move-wsus-30-to-a-new-server/comment-page-1/#comment-903