Microsoft has announced that they will be releasing Beta 3 of Windows Longhorn in the first half of 2007.
It will be feature-complete, and the first public beta of the server operating system.
To get notification of the beta release, simply sign up at Microsoft’s website
Hint: Look for this text on the bottom right: “Register to be notified of Windows Server “Longhorn” Beta availability“
When it is available you will receive an email that tells you how to obtain the beta.