You can put a preloader at the start of the SWF you are
loading, that way your screen isnt blank, the user can see
something is actually happening and if you use your immagination
you could even make a little game / interactive widget to keep them
entertained whilst the new swf loads.
I’ve seen some sites that keep the existing page loaded
until the new one is ready – a preloader keeps the viewer
informed that something is happening. Is this possible with
external SWFs or is it a timeline technique?