The community site for Silverlight will go live (or "light up") on April 30th at http://www.silverlight.net/
At this time it also sounds like like a beta (Updated from the Feb CTP of WPF/E) will be released in conjuntion with Mix07.
A few Microsoft blog posts to pay attention to:
Introducing Microsoft Silverlight
Top 10 Questions about Silverlight and Media
Introducing Expression Media Encoder
AGhost.. hiw did we miss that!? http://blogs.msdn.com/mharsh/archive/2007/04/16/microsoft-silverlight.aspx
Also keep and eye on the office site: http://www.microsoft.com/silverlight
Yep.... Mix is gonna be fun!