I just finished uploading a new tutorial that shows you the cleanest, most reliable way of preloading your ActionScript 3 movies. Like most things in Flash, there a many different ways of preloading your main content file. This approach takes a lot of the guesswork out of it and instead lets you focus more time on actually creating your movie, rather than worrying how it will preload. Check it out at http://www.gotoandlearn.com.