function imageSwap (img_name, onOrOff) {
	if (onOrOff == 'on') {
		onImage = eval(img_name + "_on");
		document[img_name].src = onImage.src;
	}
	else if (onOrOff == 'off') {
		offImage = eval(img_name + "_off");
		document[img_name].src = offImage.src;
	}
}