EDIT 9/16/2009: We have now published fixes for this problem and have an updated blog post about it. Please go here to read the updated information.
We have learned of and analyzed the problem where the Exchange 2007 SP2 installation can fail during the prerequisite check stage. The installation can fail for both the upgrade or for new installation of Exchange 2007 SP2.
In the Exchange Setup log you can see that setup is failing with the following error:
[ERROR] Cannot find at least one domain controller running Windows Server 2003 Service Pack 1 or later in domain 'DC=DCName,DC=com,DC=DCName'. This could be the result of moving domain controller objects in Active Directory. Check that at least one domain controller running Windows Server 2003 Service Pack 1 or later is located in the 'Domain Controllers' organizational unit (OU) and rerun setup.
This can happen in the following scenarios:
You are installing or upgrading to Exchange 2007 SP2 in an Active Directory forest that has only Windows Server 2008 R2 Domain Controllers
You are installing or upgrading the Exchange 2007 SP2 in an Active Directory forest that has windows server 2008 R2 Domain Controllers as well Windows Server 2003 domain controllers that are not updated to at least Windows Server 2003 SP1.
You are installing or upgrading to Exchange 2007 SP2 in an Active Directory forest that has multiple domains with Windows 2003 SP1/SP2 domain controllers, but the forest root domain has only Windows Server 2008 R2 Domain Controllers.
What are we going to do
Windows Server 2008 R2 is not widely available yet. Once Windows Server 2008 R2 is widely available, Exchange team will release a web update for the Exchange server 2007 SP2 Setup prerequisite XML files, which will add Windows Server 2008 R2 as a supported Active Directory Domain Controller. Until then, please bring up a domain controller that either has Windows Server W2003 SP1+ or Windows Server 2008 installed in your labs where you are testing Windows Server 2008 R2.
We will post more information about the fix when it becomes available.