Swf2XNA is now live! This is an open source (BSD) program that allows you to make Windows/XBox/Win7 games by leveraging Flash for assets and layout, as well as using Box2D visually. It makes 2D games in XNA quite simple to make!
There is a reasonable amount of documentation, some videos, and a lot of sample code and components. If you have any questions, feel free to email or ask on twitter (I’m there more often than anywhere – @debreuil).
Getting Started with Swf2XNA