System Center - Virtual Machine Manager is now publicly available.  The new licensing model is $860 per physical host and included unlimited VM’s running on that host.  
- http://www.microsoft.com/systemcenter/scvmm/default.mspx

Benefits include:
• Centralized deployment and management of virtual machines
• Intelligent Placement analysis to determine the best servers for virtualization
• Quick physical-to-virtual and virtual-to-virtual conversion
• Ease of use with a familiar interface and seamless integration with other Microsoft products
• Faster deployments with administrator-managed self-service provisioning
• Resource efficiency with server consolidation and increased processor utilization
• Quick automation via PowerShell scripting integration

The updated roadmap includes support for VMWare and Xen VM’s.  This means:

From a single console and a single command-line you will be able manage Virtual Server, Windows Virtualization (Viridian), VMWare and Xen.

VIRTUAL MACHINE MANAGER BLOG: 
http://blogs.technet.com/virtualization/archive/2007/09/06/system-center-virtual-machine-manager-huge-announcements.aspx