So there you have it, Windows Server 2008 R2 will not Support Exchange 2007 running on it, however if you are running Windows 2008 R2 domain controllers you will be unaffected. Several posts on this on the net but the best most reliable public reference i have found is here: http://social.technet.microsoft.com/Forums/en-US/exchangesoftwareupdate/thread/1f0be2c7-0de0-492a-9cfd-18cdc5891bc8