How do i externally control an xml photogallery

Hi i have a MC that load another MCwith an XML photogallery and i was wondering how could i control externally this gallery.
Basically if i want different button of the MC to control the MC with the xml photogallery , example i want button 3 to load the xternal gallery.swf and to load image 2 from the xml…
i know is confusing and i am not even sure if it can be done.
Any help would be awesome.