See below ...

Where "bkgdMC" is the instance name of the empty movieclip you call your XML from.


Stage.align = "TL";
Stage.scaleMode = "noScale";

var stageListener:Object = new Object();
Stage.addListener(stageListener);

setBackground();

stageListener.onResize = function() {
setBackground();
};

function setBackground() {

var middleX = Stage.width/2;
var middleY = Stage.height/2;

bkgdMC._x = topX;
bkgdMC._y = leftY;


bkgdMC._width = Stage.width;
bkgdMC._height = Stage.height;

bkgdMC._xscale = bkgdMC._yscale = Math.max(bkgdMC._xscale, bkgdMC._yscale);
}