I have a Windows Server 2003 (no Service Packs installed). It functions as a DC but has also an older Exchange Server installed.
I've set up a Windows Server 2008 R2 in hyper-v to move the DC to that new server (transitioning). I know it is not good but Exchange Server 2010 will also be installed on that new 2008 R2 server. I've already run the adprep.exe commands on the Windows Server 2003.
My question now: Should Exchange Server 2010 be installed first on the new 2008 R2 before I run dcpromo or is it better to install that Exhange Server after making the 2008 R2 server a DC?
(+ do you have some good resources on how to migrate Exchange Server 2003(?) to Exchange Server 2010?)
Microsoft supports, but doesn't recommends installing Exchange 2010 on DC. Follow this article to migrate AD and this to migrate Exchange.
You should never install Exchange server on a DC. Since you are already in the process of using Hyper-V, there is absolutely no excuse for not installing Exchange into its own VM.