Try Microsoft Virtual Server 2005
Virtual Server 2005 is a new virtual machine solution designed for the Windows Server 2003 platform. Virtual Server 2005 helps increase operational efficiency in software test and development, legacy application re-hosting, and server consolidation scenarios. Download an evaluation copy and try it for yourself.
This is a cool product, a great way to test and learn about Networked Systems. Virtual Server 2005 is Launching in two weeks in NYC along with the latest version of MOM.