Microsoft has released the Enterprise version of Vista (x86 and x64 version). It makes use of the new VA 2.0/MAK (Volume Activation 2.0/Multiple Activation Key) as Volume License Key system.
Gone are the days where you could install XP on VMware Workstation and test/snapshot/copy/delete/play/etc. with it. You have to activate this one :). Only a number of activations is allowed. I'm assuming they will use the same Licensing mechanism for Windows Server 2007 (Longhorn).
Download (and activate ;)) it now on http://www.microsoft.com/technet