If everything goes as planned over in Redmond, Microsoft will have the first test release for Windows Server 2008 available next week. At this week's IDF, Microsoft made the announcement along with another regarding Viridian, which this test release will include:

The release candidate will include a test version of software code-named Viridian and formally called Windows Server virtualization. This "hypervisor" allows multiple operating systems to run simultaneously, a useful technology in improving server efficiency and eventually leading toward more flexible data center operations.
They may release the test version to a limited public, though even if they do not the actual release is only 6 months away. This announcement from Microsoft comes after a delay in August that pushed the release into 2008.