http://www.winsupersite.com/showcase/longhorn … review_2005.asp

This is winsupersite so uhhh, take it with a grain of salt.

Longhorn Starter Edition
Longhorn Home Edition
Longhorn Media Center Edition
Longhorn Professional Edition
Longhorn Small Business Edition
Longhorn Mobility/Tablet PC Edition
Longhorn Premium Edition

None of these product names are final, of course, and all versions except Starter Edition will ship in both 32-bit (x86) and 64-bit (x64) variants.

Yikes! That's alot of different version of LongHorn. Where's the LongHorn Alpha ver? 😉