function switchMenu (id) {
	var elm = document.getElementById(id);
	if (elm!=null){
		if (!isClass(elm,'collapsed')) {
			appendClass(elm,'collapsed');
			setImage(elm.id + '_image','collapsed');
		} else {
			switchClass(elm,'collapsed','');
			setImage(elm.id + '_image','expanded');
		}
	}
}

function preloadImages() {
	if (document.images) {
		menuImages['expanded'] = new Image();
		menuImages['expanded'].src = 'images/chapter_open.gif';
		menuImages['collapsed'] = new Image();
		menuImages['collapsed'].src = 'images/chapter.gif';
	}
}


function setImage(id, src) {
	var img = document.getElementById(id);
	if (img!=null) {
		img.src = menuImages[src].src;
	}
}

var menuImages = new Object();
preloadImages();