i'm due to replace an ageing Dell Tower server running AD on Windows Server 2003 SBS with a new rackmount server running Windows Server 2008 R2
they run an Active Directory network with mostly XP SP3 clients with the odd vista or Win 7 client, they all currently run local profiles but we intend to convert them to roaming profiles because they are mostly desktop clients
we are actually retiring exchange as the client migrated to google apps a month or so ago.
we are trying to make the change as seamless as possible on the client side, so i'm guessing something along the lines of setting up new server to be a slave DC then promoting it to master status and then moving the shared files over
I would recommend following this guide and skipping any steps related to migrating Exchange or Sharepoint.
http://technet.microsoft.com/en-us/library/sbs-2008-2003-migration(WS.10).aspx
Your process sounds fine to me though admittedly I haven't done anything with SBS2003 before.
At this point you should be set to decommission the old server however I must admit I have little idea how this is achieved with SBS2003. One assumes that the roles can simply be uninstalled but I'm guessing.
Run DCPromo on the SBS2003 box and follow the instructions to remove Active Directory from the server.
Hopefully that's a decent intro. If you're running Exchange 2003, you will need to commission a new server and migrate mailboxes to the new server before transferring the FSMO roles.
NB: Once you have moved your FSMO roles and decommissioned the SBS server as a Domain Controller, you've got a grace period of 7 days to fully decommission the server before it starts shutting itself down, as per this doc. http://support.microsoft.com/kb/555087
-Lewis