Vista Starter -- Streamlined version meant for low-powered PCs in developing nations.
Vista Home Basic -- For those content to browse the web, use email, and create and edit basic documents from their PC. Includes destop search and security tools.
Vista Home Premium -- Includes everything in Basic but also includes the Aero graphical interface, Media Center functionality, and ability to connect to Xbox 360. The version most of us will own at home.
Vista Business -- The basic version for companies of all sizes with tools to help organizations manage their PCs.
Vista Enterprise -- Includes everything in the basic business version with improved encryption and BitLocker system to keep data from being read on a stolen computer.
Vista Ultimate -- All the features of Home and Business in one.