Free Virtualization Software 

Microsoft Virtual PC – free software virtualization  (Virtual PC lets you create separate virtual machines on your Windows desktop)

VMware Server Virtualization – Virtual Machine  (is a hosted virtualization platform that installs like an application on any existing server hardware & partitions a physical server into multiple virtual machines. )

VirtualBox free x86 virtualization  ( VirtualBox is an extremely feature rich, high performance product for enterprise customers, it is also the only professional solution that is freely available as Open Source Software)