When you press Start / Help and Support / Getting Started / Installing and Upgrading the Operating System / How to / Prepare for upgrades in a domain containing Windows 2000 domain controllers, step 4 contains:

Disconnect the schema master from the network and do not reestablish the connection until step 9 in this procedure.

The above statement is incorrect.

To upgrade a Windows 2000 domain controller to Windows Server 2003, see How do I upgrade Windows 2000 domain controllers to Windows Server 2003 and how to add new Windows Server 2003 domain controllers to Windows 2000 domains?