If during the site hierarchy upgrade process you intend to consolidate some or all of your existing Microsoft Systems Management Server (SMS) 2003 sites, to change the structure of your existing SMS 2003 hierarchy, or to upgrade some or all of your server hardware, you should use the side-by-side upgrade method to upgrade your hierarchy.
Use the following procedure to perform a side-by-side hierarchy upgrade.
To perform a side-by-side upgrade
Hierarchy upgrades must begin at the central site. Begin by either upgrading your existing SMS 2003 central site to Configuration Manager 2007, or create a new Configuration Manager site and configure the original SMS 2003 central site as child site of it.
Begin transitioning the site boundaries from the SMS 2003 sites to the new central site or new Configuration Manager primary sites as they are installed and the SMS 2003 sites are consolidated or decommissioned.
Upgrade SMS 2003 Advanced Clients by installing the Configuration Manager client on assigned computers.