It really seems the russian virtualization startup Parallels beaten Microsoft on its own game and the market leader VMware as well, releasing before competitors an update (build 2112) for its Workstation product which fully supports Windows Vista, completed just one week ago and already available for MSDN subscribers.
The update is automatically downloaded, free of charge, for current customers thanks to product auto-update feature.
At this point Parallels Workstation is the only virtualization solution officially supporting Vista as guest and host OS.
Download it here.