The seven editions will each be designed to cater for a different Windows user market, and will include Home Edition, Premium/Media Center Edition, Professional Edition and Small Business Edition. Additionally, there will be a `Longhorn "Uber" Edition` that will contain the functionality of the Home, Premium, Pro, Small Business, and Tablet PC Editions. On the other end of the scale, there will be a Starter Edition that will cater for the lower end of the market, offering a stripped-down, lower-cost version of the operating system.
Please remember that Microsoft has, as yet, confirmed none of this. It remains rumour, and even if based in truth (which it likely is) Microsoft have changed their plans many times before.