In this model there are various possibilities for the existing network set up:
If the existing server runs Windows Server 2000, Windows Server 2003, or SBS 2000, you can update it so that all existing data and settings are preserved. The network configuration of the server is always available in this case and is taken over by SBS 2003.
If the existing server runs Windows NT 4.0 Server or SBS 4.5, you will have to carry out a migration. In this case a fresh installation is done on a new system. The existing data and settings are then transferred from the old to the new system. Migration is also possible from an existing Windows Server 2000/2003 or SBS 2000.
If there is already a server in the network that is neither set up as a domain controller nor meant to become one, you must do a fresh installation of SBS and configure it as a domain controller. The existing server can then be added to the SBS network as a member server.