I'm pretty sure I know the answer to this but I wanted to check first as I'm not an expert on AD.
I have two windows server 2003 machines in the same domain. They are both domain controllers (primary and backup). The primary 2003 machine is running Exchange 2003.
I am going to be upgrading to Exchange 2010, using instructions I found in an excellent article here on EE.
One of the first steps in the procedure is to connect the Windows 2008 machine to the 2003 domain and make it a member server and then a DC.
Since I already have Primary DC and a backup DC (Server 2003 machines) is it OK if I connect a Windows 2008 machine and make it a DC also? Or should I remove the backup 2003 DC machine and THEN add in my 2008 machine as the backup DC?
The end result of all this will be that both 2003 machines will be going away and I will have two 2008 machines (Primary DC, with Exchange 2010 and backup DC with Exchange 2010 [I know it's not a best practice])
One more note, the 2003 machines also have DNS on them.