Ask and you shall receive - Exchange 2007 SP3 w/support for Windows Server 2008 R2 Now Available
http://msexchangeteam.com/archive/2010/06/21/455145.aspx

I am very pleased to let you all know that Exchange Server 2007 SP3 is available for download. As we highlighted in Updates to the Exchange Supportability Matrix this past November, this third service pack for Exchange 2007 enables Exchange 2007 to be installed on the Windows Server 2008 R2 version of the operating system. We heard you loud and clear that this is enormously important to our Exchange 2007 customers, so we worked quickly to deliver SP3 in order to meet this requirement.

Download Exchange 2007 SP3 here.