Preloading in flash 2004

I know there is probably a thousand posts about this but I searched and couldn’t find anything so please hear me out…

I know there is a preloader component but I would like to make a custom animations for the preloader. Is there a way to make a movie clip that plays when something is downloading and stops when it isn’t? I would like a movie clip of a tree growning that stops and starts depending on the downloading rate and when the it is completely loaded the animation would be completely done.

Does anyone know what I mean? And also, can someone tell me the AS that allows me to tell the precent of the preloader in Flash MX 2004? Thanks.