Now you can experiment with Avalon and Indigo yourself, using Visual Studio 2005 Beta 2! Download the Release Candidate of Beta 1 here. It integrates with either the Express or full version of VS2005 Beta 2.
[Update: Here's every link you could possibly need to get started!]
As I discussed last week in the WinFX talks (and will certainly continue to discuss in future), Avalon is the code name for Microsoft's unified presentation framework, and Indigo is the code name for Microsoft's unified programming model for building connected systems.