Licensing. It can be a headache, it is often misunderstood and things are different in the virtual environment. There are some great virtualization specific licensing resources I wanted to share to help you navigate these waters.
First of all there are two calculators available online. Calculator 1 lets you interactively build virtual machines running multiple Microsoft server products to estimate the licenses and costs for Windows Server by edition (Standard, Enterprise and DataCenter) and many Microsoft server products. It starts with configuring your server based on virtualization technology, sockets and clustering requirements, and then builds the virtual machines.
Calculator 2 provides two ways to estimate the number and cost of Windows Server Standard Edition, Enterprise Edition and DataCenter Edition licenses needed for your virtualization scenarios to help you determine the most cost-effective edition of Windows Server.
You can find both calculators at http://www.microsoft.com/windowsserver2003/howtobuy/licensing/calculator.mspx
The licensing team has also produced this video that explains virtualization licensing in depth. It is well worth the 25+ minutes as there are plenty of examples and scenarios covering Windows, SQL, multi-core, multi-CPU and more...
As always feel free to email us if you need further clarification!