I just noticed that Scott Schnoll posted this on his blog!
This preliminary release of the Exchange 2007 SDK Documentation and Samples provides new and updated documentation and samples for building applications that use Exchange Server 2007 Beta 2. Use the Exchange 2007 SDK Beta 2 to help you develop collaborative enterprise applications with Exchange.
Get it now at http://www.microsoft.com/downloads/details.aspx?FamilyID=8c32d5ee-a071-459e-843d-8ede0a9582b3&DisplayLang=en.
- Nino Bilic