function rollImage(action, imageName){
	if(imageName.length > 0){
		var item				= eval("document." + imageName);
		if(action == "on"){
			item.src 			= "images/nav_" + imageName + "_on.jpg";
		}else{
			item.src 			= "images/nav_" + imageName + "_off.jpg";
		}
	}
}