How to keep a movieclip centered?

programming flash
1

In this site:
http://www.duffy.com/

If you play with the size of the window of the browser, the main MC always centers itself accordingly how can I do it?

Thanks

2 
stage.scaleMode=StageScaleMode.NO_SCALE;
stage.align=StageAlign.TOP_LEFT;
align();
var clip=new Clip();
stage.addEventListener(Event.RESIZE,align);
private function align(event:Event=null):void {
    clip.x=(stage.stageWidth - clip.width) / 2;
    clip.y=(stage.stageHeight - clip.height) / 2;
}
3

Thanks!

what is the progressbar?
is this supposed to be the instance name of the MC?

4

Yes, I have just copy/pasted the code

5

Thanks a lot!