Here's a good brief overview of how to begin creating Avalon apps.  It promises to be followed by two more articles on the topic.
 
Avalon, the nascent framework for building next-generation user interfaces in Windows Vista, is available now in beta, but you don't have to wait for Vista (a.k.a. Longhorn) to get started. We unpacked it early in order to give you a jump start on building the UIs of tomorrow.

Read on...