Wait a minute here.... 
What do computer accounts in an NT4 domain have to do with disabling NT4 user accounts in the same domain? Nothing from what I can see. If you migrated all of the NT4 user accounts, then disable the NT4 user accounts. As long as the NT4 domain trusts your new account domain, users can logon using the AD user account from the NT4 domain workstation.
What am I missing???
