I love Virtual PC! Now I can do something more unique with my older workstations, one with Redhat and the other with Windows 2003 Server, since I now have Virtual PC where I can have several "virtual installs" of operating systems that run on my Windows XP Pro SP2 system!
I have 2 Windows 2003 server virtual installs (one with Fitnesse, PHP5 and the Netbeans IDE running on it and the other with Visual Studio 2005 Beta 2) and am installing SUSE Linux 9.3 in a separate install next!
This is most useful when doing development R & D on various OS/platform applications. Did I already say that I love Virtual PC?