The Active Directory Migration Tool v3.0 has just been released. I’ll have to add this to my list of things to check out.

The Active Directory Migration Tool version 3 (ADMT v3) simplifies the process of restructuring your operating environment to meet the needs of your organization. You can use ADMT v3 to migrate users, groups, and computers from Microsoft® Windows NT® 4.0 domains to Active Directory® directory service domains; between Active Directory domains in different forests (interforest migration); and between Active Directory domains in the same forest (intraforest migration). ADMT v3 also performs security translation from Windows NT 4.0 domains to Active Directory domains and between Active Directory domains in different forests.

http://www.microsoft.com/downloads/details.aspx?FamilyID=6f86937b-533a-466d-a8e8-aff85ad3d212&DisplayLang=en

Update: ADMT3 runs on MSDE. It installs MSDE onto the server but then curiously gives you the option to use MSDE or an existing SQL Server.