Cutting straight to the chase, below, you can find a plethora of unseen visuals relating to Microsoft's Windows platform. There's everything from icons to packaging prototypes:
Robert Stein III: Head 3D persona at Microsoft.
Also, don't forget to check out Robert's work on turbosquid.com where you can purchase whatever you'd like. A couple of links that may interest you are:
View: Full postMicrosoft, Windows, UI, Window UI