placeObjects = function() {
	var sw:Number = Stage.width;
	var sh:Number = Stage.height;
	var msw:Number = Math.round(sw * .5);
	var msh:Number = Math.round(sh * .5);

	//place an object to the center of the stage
	yourObject._x = msw - (yourObject._width * .5);//... horizontally
	yourObject._y = msh - (yourObject._height * .5);//... and vertically
};
placeObjects();//invoke the function

//add a stage-resize Event listener
var tfmSl:Object = new Object();
tfmSl.onResize = function() {
	placeObjects();
};
Stage.addListener(tfmSl);