Microsoft redesigned the Vista home page with lots of new information. It also provided the PDC05 screenshot gallery where in you can find cool screen shots of Vista, office 12, IE7, Digital Locker, Workflow and Expression (MAX is missing though).
Also, just happen to check Windows Vista UX Guidelines available for download from Vista Download center from Microsoft. This is a preliminary draft of the Microsoft Windows Vista User Experience Guidelines. These guidelines contain information on What’s New in Windows Vista, design principles, guidelines for controls, text, windows, and aesthetics. They will help designers and developers create high quality, consistent Windows Vista applications.
You can also find a white paper on How to build a great Windows Vista app from here.