Collision Detection

Hi,
I have had a look around in the forum but cant find what Im looking for.

Basically I have a multiple amounts of the same movieclip dropping into the stage at a random x point and then they tween left and right and find the mouse point and tween to that. Im using this kind of tween.

Code:
Tweener.addTween(this, { y:destination, time:speed, transition:"easeOutBounce", onComplete:bounceInFinished } ); 

What I need is a detect a collision between them so if they hit each other they will perform some sort of action.

Any one hav ne good tuts or examples of this ?

Thanks