Preloader for Attach movie

Since i understand when i need to make a preloader for a external .swf . then i need to place the preloader in the external file. ( i misunderstood that i need to put all preloader in the main swf b4) .
so now … i have a question. can i put a preloader in the movie clip that in library? like when i press the button, then will attach a movie clip( or movie symbol) and will the preloader run?