Microsoft has officially confirmed that there will be six versions of Vista -Mydrivers.com

As previously announced, Windows Vista will be divided into six versions based on how the computer is used rather than hardware specifications, including one basic edition, two home editions, two enterprise editions and one Ultimate Edition. They are Stater, Home Basic, Home Premium, Business, Enterprise and Ultimate. Unlike Windows XP, the 64-bit, Media Center, and Tablet PC versions of Windows Vista will not be available separately; these features will be integrated into different versions of Windows Vista.