Microsoft has put together a list of online resources to help developers get started with creating Windows 7 applications, including links to application compatibility tool, Windows SDK, managed code for Windows 7 APIs, and the training kit. See more detail here. The training kit includes many sample Windows 7 applications and presentations.
Also, you can download and run a reference Windows 7 application called “PhotoView” at the MSDN site. The application features the Image Viewer, a WPF application that runs on XP. But when you run the same application on Windows 7, it unlocks new technologies such as Taskbar, the Sensors and Location Platform, and Multitouch, as well as “old” Vista friends such as Application Recovery and Windows Search.