One of my colleagues, Rick Claus, is currently posting a series on migrating your enterprise from NT4 to Active Directory.
He currently has posted parts 1, 2, and 3 of a 7 part series.
The posts so far:
NT4 to AD In-Place Migration - Are YOU a candidate? (In-Place Migration - Part 1)
How much of an AD design required before a migration? (In-Place Migration - Part 2)
Creating the Lab environment for your AD (In-Place Migration - Part 3)
Expect to see a couple of posts each week for the next couple of weeks.
If you have any comments, head over to Rick's Blog: http://blogs.technet.com/rclaus/