According to the "Windows Vista Product Guide", a 334 page (!) summary of all editions, there are a variety of Vista editions available: Home Basic, Home Premium, Business, and Ultimate. There is also an Enterprise edition geared specifically at large organizations and I.T. Administrators of these organizations.
Although there are a variety of different Windows Vista versions, but truly they are divided into 2 camps: business and home. This makes sense in that management and functionality differ between home and work usage. Of course there are many similarities, but in general, home systems are used for personal web surfing, checking personal email (sometimes work email via web mail), downloading various multimedia files, maybe banking online, etc. Work needs vary widely, but usage of Microsoft Office is very common, as are specified custom applications. For example, a real estate company would be using real estate listings (MLS) software but an accounting firm would use something like Microsoft Dynamics. At work, centralized administration is key in order to monitor licensing and other items. At home, software usage tends to be much lighter and is basically managed by 1 person for the use of a family.
With this in mind, the 2 home editions available are Home Premium and Home Basic. The Basic version has the Photo Gallery, Search, Easy Transfer, Windows Defender, and Internet Explorer. Premium has all of that plus the following: Media Center, Aero, DVD Maker, Backups, Gaming support and Tablet support. The Ultimate version, per page 10 of the Product Guide ...
"Windows Vista Ultimate is the first operating system that combines the advanced infrastructure of a business-focused operating system, the productivity of a mobility-focused operating system, and the digital entertainment features of a consumer-focused operating system. For users who want their PC to be great for working at home, on the go, and at the office, Windows Vista Ultimate is the no-compromise operating system that provides it all."
Windows Vista Business and Enterprise are geared towards large organizations. They include the same features as the previously mentioned ones, plus the Business edition offers: shadow copy, Group Policy and Domain functionality, and some fax/scan help. The Enterprise offers the aforementioned, plus: Windows BitLocker Drive Encryption, all world languages, and 4 virtual OS license. In other words these 2 are pretty much the same. The main difference comes in licensing terms. Many large organizations (say, over 100-200+ users, going up into the thousands and thousands) have specific licensing terms through a program called Software Assurance. But that is neither here nor there.
Finally, there is a "Starter" edition listed for developing markets. It is the most basic of editions and is not offered for sale in many places.