Can you run Exchange 2007 SP1 on Server 2008 R2?

Not yet. From the Exchange team blog: "As I recently blogged about, we will be adding support for Exchange 2007 on the Windows Server 2008 R2 platform. While we had hoped to add this application/operating system combination quickly, unfortunately adding this support requires code changes to setup in Exchange 2007. Therefore, our vehicle for adding this support will be via a third Service Pack for Exchange 2007 in the second half of calendar year 2010." http://msexchangeteam.com/archive/2009/11/30/453327.aspx