If you used ADMT v 2.0 then you need to see ADMT v 3.0

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.

I personally used ADMT v2.0 to migrate 5400 Users with password from NT4.0 to 2000 and the migration was successfully. and i used it to migrate 1000 users from 2000 to 2003. I saw my friend doing a full migration from NT4.0 to 2003 with desktops been joined to the new domain without changing of their profiles, also he migrated Directory Services from 5.5 to 2003.

I love this utility, and for you to start love it you need to download it & read about it :):)