Longhorn Starter Edition
Analogous to Windows XP Starter Edition.
Longhorn Home Edition
Analogous to Windows XP Home Edition.
Longhorn Premium/Media Center Edition
A premium superset of Home Edition that includes the Media Center functionality. Similar to XP Media Center Edition.
Longhorn Professional Edition
Analogous to Windows XP Professional Edition.
Longhorn Small Business Edition
A new product edition aimed at the small business market. Currently very similar to Professional Edition.
Longhorn Mobility/Tablet PC Edition
Analogous to Windows XP Tablet PC Edition.
Longhorn "Uber" Edition
A new product edition that bridges the consumer and business versions and includes all of the features from the Home, Premium, Pro, Small Business, and Tablet PC Editions (but not Starter Edition).
Uber Edition!!! Now we're talking!