Microsoft virtualization license rules for Windows 2003

I recently came across some new licensing rules for Windows 2003 Server in regards to virtual images.

The virtualization use rights vary by edition of Windows Server. Standard Edition grants the use rights to run a single virtualized instance of Windows Server Standard Edition. Enterprise Edition grants the use rights to run four instances of Windows Server that may be a mix of Standard Edition and Enterprise Edition. Datacenter Edition is licensed per processor and grants use rights to run an unlimited number of virtualized instances of a mix of Standard Edition, Enterprise Edition and Datacenter Edition.

You can try out Microsoft's own licensing calculator and learn more.