Here is simple image loader example in AS3:

import flash.display.*;
import flash.events.*;
import flash.net.*;

var loader:Loader = new Loader();
var request:URLRequest = new URLRequest("image.jpg");
loader.load(request);
targetMC.addChild(_loader);
loader.contentLoaderInfo.addEventListener(ProgressEvent.PROGRESS, onProgress);
loader.contentLoaderInfo.addEventListener(Event.COMPLETE, onComplete);

function onProgress(event:ProgressEvent):void {
    var percentLoaded:Number = event.bytesLoaded/event.bytesTotal;
    trace("Loading: "+percentLoaded+"%");
}

function onComplete(event):void {
    trace("Complete loading");
}