Need to apply a mask to loaded swf

this is what I need to fix:  http://mespinach.com/needmask/

this is my code I've been looking all over for an example of setting a mask using AS2

I have a container MovieClip I create dynamically I've tried to attach a movieclip to the container then set mask before loading the swf

I would like to know how to dynamically generate a mask or use a symbol from the library or stage if need be whatever works.

This is my code.

var container:MovieClip = createEmptyMovieClip("container", 3);
var mcLoader:MovieClipLoader = new MovieClipLoader();

mcLoader.addListener(this);
mcLoader.loadClip("slideshow.swf", container);

function onLoadInit(mc:MovieClip) {
    container._width = 600;
    container._height = 400;
    container._x = 200;
    container._y = 100;
}