What does this mean?  You'll be able to try out using hypervisor.  The biggest advantage of hypervisor is that you can run multiple virtual machines on the base hardware (not on top of the OS).  For more information about hypervisor, check out this webcast: http://msevents.microsoft.com/CUI/WebCastEventDetails.aspx?culture=en-US&EventID=1032284286&CountryCode=US

for more information on the anouncement, go to: http://blogs.technet.com/canitpro/archive/2007/09/13/wanna-get-your-hands-on-windows-server-virtualization-viridian.aspx

Also, check out an overview screencast on Keith Comb's blog at: http://blogs.technet.com/keithcombs/archive/2007/09/13/windows-server-2008-screencast-virtualization-10-minute-tour.aspx