Comunicating between 2 external swf movies

hi,
I have 2 external movies that load when a user clicks a button. movie 1 loads into myMC1 and movie 2 loads into myMC2. How do I make a button in the external movie that loads into myMC1 comunicate with the the external movie in myMC2? I know it’s all about paths but nomatter what i try, it doesn’t seem to work. Thanks in advance!!!