I've released a library that ties the Box2D Flash physics engine in with Flint. With a few lines of code, you can have Box2D's full power while still using all the Flint primitives you are used to.
More details are here, with a demo available.
If you click twice on the demo, you'll find the "Flint only" example, aimed at Flint users. I append the bulk of the source for that to give you an idea how simple it is to get started.
BodyRenderer.defaultScale = 10;
//Create a Flint emitter and initialize it with some standard particles stuff
emitter = new Emitter2D();
emitter.counter = new Steady( 15 );
emitter.addInitializer(new Position(new DiscZone(new Point(0,0),30,30)));
emitter.addActivity(new FollowMouse(this));
emitter.addAction(new MutualGravity(3, 100));
emitter.addInitializer(new Velocity(new DiscZone(new Point(0, 0), 10, 10)));
emitter.addInitializer(new ImageClass(Dot, 10));
emitter.addInitializer(new Lifetime(2, 20));
emitter.addAction(new Fade());
emitter.addAction(new Age());
//Use a physics activity, and keep a reference to it.
var physics:Physics = new Physics();
emitter.addActivity(physics);
//Lets give the position solver a bit more pep, as we are creating lots of overlapping shapes
physics.positionIterations = 30;
emitter.addInitializer(new CollisionRadiusInit(10));
emitter.addInitializer(new CircleInit(physics.world));
renderer = new DisplayObjectRenderer();
addChild(renderer as DisplayObjectRenderer);
renderer.addEmitter(emitter);
emitter.start();
I'm afraid for more complicated effects, you'll actually need to learn something about Box2D, but nonetheless, I think it's a fairly easy system to use.]]>