How add a Windows 2003 to a Windows 2000 Active Directory?

These days, I took a lab test, add a Window Server 2003 to a pure Windows 2000 Active Directory. I found there is an relative error in Microsoft Knowledge Base.

According support.microsoft.com/kb/278875, if you want to add a Windows Server 2003 into a exist Windows 2000 AD, then you just need to extend exist AD by using adprep.exe. But, after my test, it's not right.

You must upgrade the domain to "native mode" than the default value "mixed mode". Then you could join a Windows 2003 Server as DC of Windows 2000 domain.