var replace_rules = {
	'a.replace_image' : function (element) {
		var src = "images/" + element.id + ".jpg";
		var down_src = "images/" + element.id + "Dn.jpg";
		if(Element.hasClassName(element, "current_page"))
		{
			src = down_src;
		}
		element.innerHTML = "<img src=\"" + src + "\" alt=\"" + element.title + "\">";
		Element.removeClassName(element, "replace_image");
		Event.observe(element, "mouseover", hover_image);
		Event.observe(element, "mouseout", unhover_image);
	}
};
Behaviour.register(replace_rules);

function hover_image(event) {
	var target = Event.findElement(event, "A");
	if(Element.hasClassName(target, "current_page"))
		return;
	target = target.getElementsByTagName("IMG")[0];
	var src = target.src.split(".jpg")[0];
	target.src =  src + "Dn.jpg";
}

function unhover_image(event) {
	var target = Event.findElement(event, "A");
	if(Element.hasClassName(target, "current_page"))
		return;
	target = target.getElementsByTagName("IMG")[0];
	var src = target.src.split("Dn")[0];
	target.src =  src + ".jpg";
}