Retro-fitting a preloader... little help here!

Hi everyone, I know preloader questions abound in this forum, and I am sorry to add to them! I am just having a bit of trouble retro-fitting my preloader into this code.

The code below shows the launch button click function... which calls up an external swf. I just want it to preload this work, just for some reason having a hard time understanding how to make that happen. I have a preloader at the front of my site working with no problem, just having trouble figuring out how to add to this code... sorry in advance, but thanks.

stop();

next_btn.addEventListener(MouseEvent.CLICK, NextFrame);

function NextFrame (e:MouseEvent):void{
    this.nextFrame();
}

btn_close.addEventListener(MouseEvent.CLICK, closeClick);

function closeClick (e:MouseEvent):void{
    parent.removeChild(this);
}

launch_btn.addEventListener (MouseEvent.CLICK, launchClick);

function launchClick (e:MouseEvent):void{
    var request:URLRequest = new URLRequest("tw_csr.swf");
    var loader:Loader = new Loader()
    loader.load(request);
    addChild(loader);
    loader.x = -480;
    loader.y = -285;
    closeBook.addEventListener (MouseEvent.CLICK, closeWindow);
    addChild (closeBook);
    closeBook.x = 405;
    closeBook.y = 221.8;
   
    function closeWindow (e:MouseEvent):void{
        removeChild (closeBook);
        removeChild(loader);
    }
}

var closeBook:close_btn = new close_btn();