Can they be resized dynamically with JS?

If so, why wont this script work, i keep getting the warning that document.viewing has no properties.

Code:
// JavaScript Document

// resizeHeaderImages makes calls to the sizeTo() function

function resizeHeaderImages(){
	if(navigator.userAgent.indexOf('MSIE') != -1){
	var width = document.body.clientWidth / 4;
	var percentage = width/640;
	var height = 480 * percentage;
	document.image1.width = width;
	document.image1.height = height;
	document.image2.width = width;
	document.image2.height = height;
	document.image3.width = width;
	document.image3.height = height;
	document.image4.width = width;
	document.image4.height = height;
	document.viewing.width = width*4;
	document.viewing.height = document.body.clientHeight - height-30;
	}
}