function init() {
	var x = document.getElementById('mainNav').getElementsByTagName('img');
	for (var i=0;i<x.length;i++)
	{
		addEvent(x[i],"mouseover",swapIn);
		addEvent(x[i],"mouseout",swapOut);
	}
}

function swapIn() {
	this.src = "/images/all/" + this.id + "_btn_on.gif";
}
function swapOut() {
	this.src = "/images/all/" + this.id + "_btn_off.gif";
}