I started to write about this at SBS 2003 to SBS 2008 migration thoughts and issues and Active Directory Health Checks, but after some discussion with the SBS team at Microsoft we now have much more:

The Official SBS Blog : SBS 2008 Migrations from SBS 2003 – Keys to Success

The purpose of this post is to help you complete your SBS 2003 migrations to SBS 2008 successfully on the first attempt.

………………  much, much more

Use this information if you have a non-standard implementation or are concerned about the success of a migration.

ttfn

David