Good News and bad news. You have three interlocking problems. 1 – migrate from NT4 to 2k3. Lots of help available (Brien Posey, Mark Minasi both have multiple articles). Bad part is doing the prep work. Lay out your forest, domain(s), backups strategy, AND verify capability of the servers to be migrated. Hardware in servers running NT4 may NOT work under 2K3! BE SURE it will work. 2 – AD migration is either simple or very awful based on one question. Do you intend to migrate the Exhange server at the same time? If you have any choice do Exchange AFTER the AD migration. 3 – AD depends on DNS and DNS in MS is tied to the AD. Know every IP address or least the range of addresses. Hopefully you have already deprecated WINS and NetBIOS. Any service(s) depending on NetBios names to ‘find’ servers, printers is a probable break point.
While the migration services provided by outside vendors look expensive at first glance, a consultant’s help planning the AD structure can save a lot of hours (overtime).
I wish the best for this undertaking. Happy Thanksgiving and no you won’t be done by Christmas.