Chris Haaker from Geeking Microsoft writes:

As of SP2, Exchange 2003 was supported in production in a Microsoft virtual environment. Now that Exchange 2007 requires 64 bits to be supported in production and Microsoft does not have a virtualization platform that supports a 64 bit guest, Exchange 2007 is not supported in production in a virtual environment.

From the Microsoft document Technical Architecture of Exchange 2007:

Exchange 2007 and Virtualization

Exchange 2007 is not supported in production in a virtual environment; however, as stated above, Microsoft Virtual Server makes a great environment for training, labs, and demos. Exchange 2007 is supported in production environments using only the 64-bit version of Exchange 2007, and currently neither Microsoft Virtual Server nor Microsoft Virtual PC support 64-bit guest systems. Exchange 2007 is also not supported in production in a virtual environment using non-Microsoft virtualization software. For details about the Microsoft support policy for third-party virtualization software, see Microsoft Knowledge Base article 897615, Support policy for Microsoft software running in non-Microsoft hardware virtualization software.

The first 64-bit guest support is expected to be included with Hypervisor, which is an add-on for Windows Server Code Name "Longhorn" from Microsoft that is scheduled to ship within 180 days of Longhorn. Note that this is within 180 days, meaning it could ship the same day as Longhorn, or it could ship 180 days after Longhorn ships. For more information about Microsoft's virtualization plans, see the Microsoft Machine Virtualization Roadmap Chat-Transcript.

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