The fix for installation of Exchange 2007 SP2 with Windows 2008 R2 Domain Controllers is now available
MSExchangeteam blogged about the process to fix Exchange Server 2007 SP2 installation when using Windows Server 2008 R2 DCs.
We have released the updated Setup prerequisite files for the problem we wrote about in Exchange 2007 SP2 Setup fails if all domain controllers are running Windows Server 2008 R2. This fix will unblock Exchange 2007 SP2 setup in those environments.
Read more at source: http://msexchangeteam.com/archive/2009/09/15/452494.aspx