var W3CDOM = (document.createElement && document.getElementsByTagName);

var mouseOvers = new Array();
var mouseOuts = new Array();

window.onload = init;

function init() {
	if (!W3CDOM) {return; };
	var nav = document.getElementById('nav');
	var imgs = nav.getElementsByTagName('img');
	for (var i=0;i<imgs.length;i++) {
		imgs[i].onmouseover = mouseGoesOver;
		imgs[i].onmouseout = mouseGoesOut;
    var suffix = imgs[i].src.substring(imgs[i].src.lastIndexOf('.'));
		mouseOuts[i] = new Image();
		mouseOuts[i].src = imgs[i].src;
		var endpoint = imgs[i].src.lastIndexOf('.');
		var imageBaseName = imgs[i].src.substring(0, endpoint);
		var mouseOverImg = imageBaseName + "RO" + suffix;
		mouseOvers[i] = new Image();
		mouseOvers[i].src = mouseOverImg;
    imgs[i].number = i;
	}
}

function mouseGoesOver() {
	this.src = mouseOvers[this.number].src;
}

function mouseGoesOut() {
	this.src = mouseOuts[this.number].src;
}