[llllllllll]

fscommand("fullscreen",true);
Stage.align = "T" // и еще море модов =)

... а далее ...

myMovieClip.onResize = function(){
this._x = вычисляемс // может поможет System.capabilities.screenResolutionX
this._y = аналогично ...
}
Stage.addListener(myMovieClip);
Stage.broadCastMessage("onResize");