Ok. It isn’t really a migration; in reality, you are joining an SBS 2008 machine to an existing Server 2003 domain. However, since you have to do similar tasks as you do for a migration, I’m calling it that.
In short, you are following the same instructions that are found in this Microsoft Technet posting. In a nutshell:
- Prepare the domain computer, including (and especially) updates to SP 2, and confirming that you don’t have any AD errors happening
- Backup the system state on the source server at the very least
- Raise the functional AD level to Windows 2003
- Run the Migration Prep tool from the SBS media. Note that you may need to run it more than once for it to update the Forest and Domain Schemas
- Prepare the answer file
- Install SBS on the new server with the answer file on a flash drive in the machine
- Prepare to wait, but check on the SBS machine often to make sure it hasn’t stalled on the AD migration process (it will tell you if it did)
- Robocopy. Learn it, love it, and prepare a batch file to run copy scheme after copy scheme if you have multiple shared folders to move.
- The Migration tool in the SBS Console will not work. However, you can do most of the items needed (especially the updating of Users and Groups to the new schema) via the Console screen under Users and Groups. You will need to do this to show the Users and Groups in the SBS console
That is pretty much it. The rest, especially decommissioning and older Exchange server is an exercise I leave to the reader.