Q: I have been given a task that involves installing a domain controller (with GC) into a remote site. I've built a machine with Windows Server 2003. Currently, my site is running Active Directory under Windows 2000 server. Can I run DCPROMO on the Server 2003 machine while the root domain is on a lower level of AD?
A: Yes. A Windows 2003 machine can be DCPromo'ed to operate in a Windows 2000 Active Directory. However, if this is the first Windows 2003 server in the Windows 2000 Active Directory, you will need to run the forestprep and domainprep prior to running DCPROMO on the Windows 2003 machine. Windows 2003 uses a newer version of the AD Schema.
All of your Windows 2000 Domain Controllers should be on SP2 at the very least. You will need to also perform some additional steps if you have Exchange 5.5 or Exchange 2000 in your environment. Here is a step-by-step from Microsoft.
You need to be very careful about allowing replication to complete if your Schema and Infrastructure master roles are on two different servers. Don't rush things and check the event logs frequently to make sure all is going as planned. Prior to even starting, validate that you do not have any domain replication issues by reviewing the event logs, using DCDIAG or REPLMON.
This was first published in August 2005