function swapNavOn(elName){ 
	imageEl = document.getElementById(elName + "_image");
	imageSrc = imageEl.src.toString();
	imageLoc = imageSrc.substring(0,imageSrc.lastIndexOf('/'));
	imageEl.src = imageLoc + "/" + elName + "_on.jpg";
}
function swapNavOff(elName){
	imageEl = document.getElementById(elName + "_image");
	imageSrc = imageEl.src.toString();
	imageLoc = imageSrc.substring(0,imageSrc.lastIndexOf('/'));
	imageEl.src = imageLoc + "/" + elName + ".jpg";
}