I have a Windows 2000 DC and a Windows NT 4 Exchange 5.5 server. We have a 2003 Standard server built with Exchange 2003 Standard and want to migrate to the new server for exchange. We would like to keep the 2000 server our primary DC. I would like to keep exchange 5.5 and 2003 running at the same time to easily move users from one server to the next. Also, are there going to be any difficulties adding the 2003 server to our DC group? I have not yet installed Exchange 2003 just in case there are any special installation instructions. Any help would be appreciated.