Windows Vista Development Guidelines

Microsoft has released its preliminary Windows Vista user interface guidelines. It's a set of 12 rules for software developers to make use of to help encourage developers to create software for Windows Vista that have a consistent, polished look and feel.

The guide gives insight into Microsoft's views on how Windows Vista apps should look. For instance, the new Windows Vista font is called "Segoe UI" and Microsoft made this their top rule -- use this font in Vista apps. Other rules include how to work with the new Aero Glass APIs and making use of the new search features in Windows Vista.
Windows Vista User Interface Guidelines
Microsoft UX Guidelines official page