The long awaited new version of Microsoft’s Active Directory Migration Tool is now available for download from:
The most important feature of the new version is is the ability to migrate to Windows Server 2008 Functional Level domains. This was not possible with version 3.0.
If you need to copy passwords as part of your user account migration, you will also need the Password Export Server (PES).
There is a also a separate document available for download entitled “Migrating and Restructuring Active Directory Domains Using ADMT v3.1″
If you don’t like ADMT, you could also look at Quest’s Migration Manager for AD.