Being new to Flash myself, I've got two words for you:

Separate Preloader.

Do a search and you'll find some info. Any other preloader or preloading system is a waste of time. For me, anyway.

The separate preloader will create an empty movieclip into which your main movie is dumped. this new container hides your movie until it's done preloading. once finished, the container is then replaced by the main movie.

I probably haven't explained that right, but you get the gist. Separate preloaders are brilliant, and have solved all of my loading issues.

Hope that helps.