Vista Business and Vista Enterprise are targeted towards workplaces small and large, respectively. Vista Home Basic continues your usual Windows XP/98/95 family tree with some enhancements, while Vista Starter is meant for low cost computers in emerging markets. Vista Home Premium adds the Aero desktop feature, Tablet PC and Media Center capabilities and Vista Ultimate is the do-everything of the bunch, including all of the available features.
We're disappointed Microsoft didn't include Media Center capabilities across the product line. Besides the confusion factor, how are you supposed to tell your boss you need IT to install Vista Ultimate because you want to stream the HD Beat podcast while playing Project Gotham on one of the conference room projectors?