A tutorial on how to use Box2FP to integrate Flashpunk and Box2D in Actionscript, from http://www.throwthelookingglass.com.
Before using Box2FP, you should have some conception of how both Flashpunk (http://www.flashpunk.net) and Box2D (http://www.box2dflash.org). Both of these have pretty good tutorials (reading the manual of Box2D is particularly important).
Box2FP can be found at https://github.com/pdyxs/Box2FP
Go to http://www.throwthelookingglass.com/2011/06/box2fp-tutorial-making-games... for the code of the sample project.