Windows Vista Unleashed!
Just a few moments ago, I learned that Windows Vista Beta 1 is available on MSDN Subscriber downloads. How cool is that - a week before the launch date that was announced. You can also download the Windows Longhorn Professional Edition Beta 1 Windows Developers Kit.
On top of that, the official Windows Vista website has been updated with a lot of information on a variety of topics including Aero, Security, Reliability and more. Indigo has been renamed to Windows Communication Foundation. Avalon has been renamed to the Windows Presentation Foundation.
If you are interested in developing with Windows Vista, I've written a book called Professional WinFX Beta (alongside Bill Ryan, Ron DeSerranno and the lovely Alexandra Young). Here is the cover and writeup on Amazon: http://www.amazon.com/exec/obidos/tg/detail/-/076457874X?v=glance
Check out the new details here: http://msdn.microsoft.com/windowsvista/