You can visit the new Windows Vista (formally Longhorn) Developer Center and check out some cool new content and a nice user interface. In addition MSDN subscribers can download the BETA 1 bits for Windows Vista.
While not a feature complete BETA the bits will give developers a good look at the future direction of the Windows Operating System. Other BETAs will follow with even more new features.
Take a look at the User Experence section for some information about the direction of AERO and the new UI for Windows Vista.