I found this great piece of info when I was checking some feeds..
…..In Windows Vista, the two categories are Home and Business. In the Home category, Microsoft will create four product editions: Windows Vista Starter Edition, Windows Vista Home Basic Edition, Windows Vista Home Premium Edition, and Windows Vista Ultimate Edition (previously known as “Uber” Edition). In the Business category, there will are three editions: Windows Vista Small Business Edition, Windows Vista Professional Edition, and Windows Vista Enterprise Edition. In all, there are 7 product editions planned for Windows Vista
7 product edition…I hope too many version does not confuse users….
Check this article for detailed info.