Disable Buttons when loading certain external .SWFs

Hi, Ive got a main MC which contains all the navigational buttons. I then have an empty content MC which loads into it all the external .swf relating to the main navigation buttons. My question is as follows:

I would like to disable the navigational buttons on the _root MC when entering the first frame of a perticular external .swf which has been loaded in the content MC.

Hope this makes sence.

thanks in advance.