Virtualization technologies offer new ways to transform your IT
environment into a system that is more dynamic and cost effective. With
the Microsoft end-to-end virtualization platform, you can improve
nearly every aspect of the IT infrastructure management lifecycle. The
process to license Microsoft products for a virtual computing
environment is essentially the same as it is for a physical
environment, and our licensing models can help you take advantage of
the benefits of virtualization.
Learn more about Microsoft Virtualization

addition, we have included some unique license rights for certain
products that support virtualization so that you can take advantage of
existing and future virtualization technologies across the complete
Microsoft virtualization platform—including desktops, applications,
servers, and management. Examples include the following.

Windows Server 2008 Enterprise
This license allows you to run up to four software instances at a time
in virtual operating system environments (OSEs) on a server under a
single server license.

Windows Server 2008 Datacenter
This license allows you to run any number of software instances in physical and virtual OSEs on a server.

Microsoft SQL Server 2008 Enterprise Edition
This license allows you to run any number of software instances in one
physical server
and any number of virtual OSEs on the server.

Windows Vista Enterprise Centralized Desktop (VECD)
This is a flexible, subscription-based licensing option for enterprise
customers and early adopters who want to deploy Windows Vista in
virtual OSEs that are running on servers. Each VECD license allows one
user to access up to four concurrently-running instances.

System Center Server Management Suite Enterprise (SMSE)
This is a comprehensive solution for server application and platform
management across physical and virtual server environments. Along with
other System Center products, it includes Virtual Machine Manager. One
SMSE license
allows you to manage the physical OSE and any number of
virtual OSEs
on a server.

Microsoft Desktop Optimization Pack (MDOP) for Software Assurance
This is a dynamic desktop solution designed to increase Windows desktop
manageability and reduce system complexity. MDOP offers a suite of
technologies that can help reduce application management costs,
instantly deliver virtualized applications (via Microsoft Application
Virtualization for Desktops, formerly SoftGrid), and better control
desktop environments, enhancing IT responsiveness and user uptime.