i still can figure out how to resize the cover_mc when the broswer is resize.

here is the code im using

Code:
stop();

// noScale prevents content in the movie resizing (unless we tell it to!)

Stage.scaleMode = "noScale";
Stage.showMenu = false;
// LT means all positions measured from the top left hand corner
Stage.align = "TL";
// a function to be called when the movie resizes
// this will resize the background clip to fill the stage
bg_mc.onResize = function() {
	this._width = Stage.width;
	this._height = Stage.height;
};
// get the bg clip to listen for events (onResize) 
// broadcast by the stage object
Stage.addListener(bg_mc);
bg_mc._x = bg_mc._y = 0;
bg_mc.onResize();

//trace(bg_mc._height);

cover._x = Stage.width/2;
cover._y = Stage.height/2;



cover.onResize = function(){
	this._x = Stage.width/2;
	this._y = Stage.height/2;
}

Stage.addListener(cover);
cover.onResize();