Virtual Server for Free

MS Virtual Server 2005 R2
http://www.microsoft.com/windowsserversystem/virtualserver/default.mspx

http://www.microsoft.com/windowsserversystem/virtualserver/software/default.mspx

Microsoft Virtual PC 2004
http://www.microsoft.com/windows/virtualpc/default.mspx

http://www.microsoft.com/windows/virtualpc/downloads/sp1.mspx

VMware Server 1.0
http://www.vmware.com/products/server/

http://download3.vmware.com/software/vmserver/VMware-server-installer-1.0.0-28343.exe
http://download3.vmware.com/software/vmserver/VMware-server-linux-client-1.0.0-28343.zip
http://download3.vmware.com/software/vmserver/VMware-server-win32-client-1.0.0-28343.zip
http://download3.vmware.com/software/vmserver/VMware-server-1.0.0-28343.i386.rpm

Tech Doc
http://blogs.msdn.com/virtual_pc_guy/