Microsoft has made the full version of Virtual PC 2007 available for download from their web site. The program is available in both 32- and 64-bit versions, and is supported on all versions of Windows XP (except Home and Media Center Edition), Windows Server 2003, and Windows Vista.
VMware has just released version 1.0 of its free VMware Server. With VMware Server you can create and run guest operating systems (”virtual machines”) such as Linux, Windows, FreeBSD, etc. under a host operating system.