Please help with preloader and .as file

I am trying to build my first web site using pure(or almost pure) .AS file.

Inside my main fla file I have a MC with an animation that is an introduction.

I am doing this at my as file:

var animacao : intro = new intro();

and I have a function to load up the animation when a user first enter the site with this code

        private function loadAnimation():void
            animacao.x = 190;
            animacao.y = 450;
            addEventListener(Event.ENTER_FRAME, onEnterFrame);

        private function onEnterFrame(e:Event):void
            if (animacao.fim)
                animacao.fim = false;
                removeEventListener(Event.ENTER_FRAME, onEnterFrame);

this onEnterFrame event is to know when my animatin reachs the end.

Everything is working correctly except that I need to put a preloader before a load this animation but how do I do this since I am using it from my fla file?

thank you