Windows Longhorn is the next major operating system to be released by Microsoft, its is EXTREMELY alpha, and wont be released until mid 2006 at least.
At this time, asides from having a new file system that can stack E-Books by category (which uses 99% CPU), and a sidebar with an analog clock, there really isn't anything to explore in the latest released alpha (6.0.4053).
Most of the revolutionary advancements that Longhorn will have haven't been implemented yet, so there's really nothing to see, and the OS is so buggy and unstable that it really can’t be used as an OS.
The alpha is worthless to just about everybody at this time, including developers, so I encourage you not to waste your time, not to mention that it's illegal to have.
I expect great things from Longhorn, but its years away and isn't even remotely useable at this time.