I recently had to move a Windows XP pc to a new domain, taking the user's settings with him to the new setup.  I found some great instructions here (Google Groups is becoming a fast favorite of mine for troubleshooting-type issues) for migrating the user account to the new domain...I would just make one extra suggestion.  Make sure, when you copy all the files from the old profile to the new one, that you have selected all the hidden and system files as well. 

The problem I ran into was in trying to get a Business Contact Manager database migrated to the new domain.  You can't just open the database with the new profile, because it's 'owned' by the first profile. 

It turns out you can just backup the database as the 'old' user, then log in as the same user in the new domain, and 'restore' the database with BCM. 

I couldn't find documentation that said this was a preferred method, butit worked for me!