This is effectively the reverse of this scenario.
I have an SBS 2003 R2 domain with 20-odd users in it (25 CALs).
The firm is being split into two; five users are leaving. A new SBS licence and server are being purchased for the leavers. The new server will be running SBS 2008 but we could put 2003 on first and then upgrade if that makes it easier. [Well, not upgrade as such, obviously]
I can borrow a large VM server (running Hyper-V) if it will be useful to bring up temporary machines as part of the migration.
How would I set about tranferring user accounts, data, email, etc?