function preloadImages(images) {
	var imageArray = new Array(images.length);	
	for (var i = 0; i < images.length; i++) {
		imageArray[i] 		= new Image();
		imageArray[i].src	= images[i];
	}
	return imageArray;
}

function switchButton(button, buttonStr) {
	window.document.images[buttonStr].src = button.src;
}