The Migration wizard only supports migration from Windows Small Business Server

If attempting to use the migration wizard in SBS 2008 or SBS 2011 from a domain with a standard windows server you will see the message

The migration wizard ONLY works from a SBS 2003, 2008 or 2011 server.

http://technet.microsoft.com/en-us/library/gg490796.aspx

Migration guide from SBS 2003

http://social.technet.microsoft.com/Forums/en-US/smallbusinessserver/thread/f3966043-8b4e-41e5-a32b-27761d98b0b5/

Collated document for migration from SBS 2003

http://cid-c756c44362cd94ad.office.live.com/view.aspx/Susanified/Susan%20Additions%20Migrate%20to%20Windows%20Small%20Business%20Server.docx

Something that may be useful to migrate a standard server to an sbs 2011:

Go to sbsmigration.com and order the migration kit for this project. In short terms you extract the AD information from your old domain and then migrate that information to a SBS 2011 server. Advantage from this method is that your SBS 2011 server can end up with the same servername and ip address as the original server.