According to this source Mike Neil - General Manager of Virtualization, said "We expect the release candidate next week".  I've not seen this reported first-hand...so can't confirm the statement.

With its built-in server Virtualization technology, Windows Server 2008 enables you to reduce costs, increase hardware utilization, optimize your infrastructure, and improve server availability.

Built-in Virtualization to virtualize multiple operating systems—Windows, Linux and others—on a single server. With Virtualization built into the operating system and with simpler, more flexible licensing policies, it's now easier than ever to take advantage of all the benefits and cost savings of Virtualization.

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