Need to apply a mask to loaded swf

Question

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;

Answer 1

function onLoadInit(mc:MovieClip) {
    container._width = 600;
    container._height = 400;
    container._x = 200;
    container._y = 100;
     var r:MovieClip = createEmptyMovieClip("rectangles", 2);
    r.beginFill(0xcc00cc, 100);
    r.moveTo(20, 20);
    r.lineTo(160, 20);
    r.lineTo(160, 160);
    r.lineTo(20, 160);
    container.setMask(r);
change the values as your need.