I’ve decided to take a look at Box2D for Flash, cause I hope to make some games using this powerful engine, but according to the news from 1/08/10 on box2d.org, website was hacked by someone. So, right now Box 2D AS3 Manual is not available (404 Page not found), but thanks to Google, there is a cache of the manual.
З.Ы.: Actually, latest version of manual can be found here: http://box2dflash.boristhebrave.com/docs/.