Transition between levels = ooopss problem!

well, I would like to know the solution (if there is one) to this problem.
I have one main movie, and others 3 external movies that are loadded in the main , with “loadClip” command. Until now everithing is ok. But when I try to make the transitions betwenn this movies with fade in/fade out, (for example ) it does not work. I know, that I have to put a comand {setInterval()}, but I don`t know how to do it.
If anyone could give-me a simple exemple just for understan tha actionscript between this movies

thank you very much
Linu