You'll need to make the arm and gun a seperate symbol from tehmain body. Then the easiest method is to amke the arm move back frame by frame.

You could either do this on teh stage. Then copy/paste teh frames into an MC. Or do the animation in the MC first.

I use more of a cartoon style. But this tut may help you out:
http://www.studiowhiz.com/_tutorials...ndex.php?id=55

Also any other links you may find helpful:
http://www.studiowhiz.com/_boards/sh...&threadid=1275

FlashFilmMaker:
http://www.flashfilmmaker.com/Tutorials/