The first step in the actual upgrade process is to physically prepare the domains and the computers. This important step streamlines the upgrade process and makes it go as smoothly as possible.
Before adding any Windows Server 2003 domain controllers to an existing Windows 2000 forest, or upgrading any Windows 2000 domain controllers to Windows Server 2003, you need to update the Active Directory schema and prepare the network. You also have to prepare each additional domain before adding any Windows Server 2003 domain controllers.
To prepare a forest for Windows Server 2003 domain controllers, use the following procedure:
Update all Windows 2000 domain controllers ...