You want to determine if a domain controller is ready to be upgraded to Windows Server 2003.
Insert a Windows Server 2003 CD into the Windows 2000 domain controller or map a drive to the files contained on the CD. Run the following command from the \i386 directory:
> winnt32 /checkupgradeonly
The /checkupgradeonly switch simulates the initial steps for upgrading a server to Windows Server 2003. It verifies, among other things, that adprep has completed and that any installed applications are compatible with the new operating system.
Recipe 2.11 for determining if adprep has completed and MS KB 331161 (List of Fixes to Use on Windows 2000 Domain Controllers Before You Run the Adprep/Forestprep Command)