Dynamically creating instance of extended MovieClip class

Hi all,
I have recently started out with flash oop concepts and was wondering how to do create an instance of an extended movie class without dragging and dropping the clip from the library …
I have figured out this method…
for(i = 0;i<100;i++)
{var mc:MovieClip = attachMovie(“ball”,“dasd”+i,_root.getNextHighestDepth());
mc._x = Math.random() * 600;
mc._y = Math.random() * 600;
but this way I cant pass arguments to the constructor function of the ball class…
any help would be highly appreciated