I am in the middle of moving a client from an old SBS2000 based server to a pair of brand new servers, with the intention of retiring the SBS server completely and moving over to Server 2008 and Exchange 2007. I have done an interim stage of running Server 2003 (with AD installed and running as a domain controller) and Exchange 2003, and have joined it to the domain and have migrated all the user mailboxes. I am now installing the second new server with Server 2008, and wanted to promote it as a DC. I have run adprep / forestPrep on the old SBS server without any problems, but when I try to run domainPrep, it complains about the domain running in mixed mode.
My question is this. Do I A) convert the old SBS to Native mode and carry on with the migrate to 2008/Ex2007, leaving the SBS2000 server in place until the end or B) migrate fully to the Server 2003, move the FSMO roles away from the SBS server and shut it down, and then move to 2008.
I have so far found no reports of problems switching from mixed mode to native, and there are no NT4, Exchange 5.5 or pre-2000 clients, which leads me to think that option A is the best way to go.