I followed the instructions in the Microsoft article "XADM: How to Create a First Administrative Group with a Different Name" (http://support.microsoft.com/default.aspx?scid=kb;en-us;q271882) so that I can install my first Exchange 2000 Server in an administrative group with a name other than First Administrative Group. When I install the server, do I have to repeat the forest or domain prep steps?
First, a quick recap: After you install a server in an administrative group, you can't move it to another administrative group. (My limited testing suggests that you can use ADSI Edit to move a server, but Microsoft doesn't support this action, so you're on your own if you try it.) By default, the first server you install into a new organization goes into the First Administrative Group. The Microsoft article you mention says to run Exchange setup with the /forestprep switch and select Exchange System Manager (ESM) as the only component to install. When prompted, create the new administrative group that you want to use.
When you later install the Exchange server components, you can select this administrative group. You don't need to redo the /forestprep operation. However, if the machine on which you installed ESM is in a domain other than the one in which you're installing your Exchange server, the Exchange server's host domain must be domain prepped. Exchange setup preps the domain automatically when you try to install the server components, or you can do the job manually at your convenience.