addEventListener(Event.ENTER_FRAME, loading);
stop();

function loading(event:Event)
{
	var bytestotal = stage.loaderInfo.bytesTotal;

	var bytesloaded = stage.loaderInfo.bytesLoaded;

	var loader = Math.round(bytesloaded*100/bytestotal);

	moviePreloader_mc.LoaderMask.scaleX = loader/100;
	moviePreloader_mc.percent2.text = int(loader)+"%";

	if (bytesloaded == bytestotal)
	{
		gotoAndPlay(2);
		
		removeEventListener(Event.ENTER_FRAME, loading);
	}
}

add every item in the library to the frame that comes after this code.

How to create a Loader

ActionScript 3