ActionScript 3.0 :: Preloader - Start MovieClip And Extend To Width Of Stage

I have a problem animating the preloader of the site I've been working on. I want a movie clip (a dark grey rectangle) to start at width = 0 and then extend to the width of the stage. But it just doesn't move, it preloads perfectly but doesn't really extend with the progress event.

Here's the code:
loadBar_mc.width = 0
var l:Loader = new Loader();
l.contentLoaderInfo.addEventListener(ProgressEvent.PROGRESS, loop);
l.contentLoaderInfo.addEventListener(Event.COMPLETE, done);
l.load(new URLRequest("Bnaider.swf"));
function loop(e:ProgressEvent):void {
[Code] .....
[URL]