Updates to the Exchange Supportability Matrix
With the release of Exchange 2007 SP2 we provided a Supportability Matrixwhich outlined the supported configurations for Exchange 2000 SP3, Exchange 2003 SP2, and Exchange 2007 (RTM, SP1, and SP2). But as many are aware, with the release of Windows Server 2008 R2 there have been a variety of questions raised about our support policies and a multitude of feedback. Two pieces of feedback occurred numerous times - the need to support Exchange 2007 on Windows Server 2008 R2 and the need to support Exchange 2003 against Windows Server 2008 R2 Active Directory servers.
Read more at source: http://msexchangeteam.com/archive/2009/11/30/453327.aspx