this.addEventListener("enterFrame",onEnterFrame);

function onEnterFrame(e:Event) {
    loadbar.width = (this.loaderInfo.bytesLoaded/this.loaderInfo.bytesTotal)*200;
    if (this.loaderInfo.bytesLoaded == this.loaderInfo.bytesTotal) {
        gotoAndPlay(2);
        this.removeEventListener("enterFrame", onEnterFrame);
    }
}

http://blog.hydrotik.com/2007/10/01/as3-useful-little-things/

As always, IE7 is stupid

AS3: Handle Preloaders in ie7

ActionScript 3