window.onload = function() {
	list = $('menu').getElementsBySelector('div[class="btn_menu"]') ;
				
	for( i = 0; i < list.length; i++) {
		list[i].onmouseover = function() {
			$('Layer2').childNodes[0].src = './img/sn_over_'+this.id+'.jpg';
			elem = null;
		};
		
		list[i].onmouseout = function() {	
			$('Layer2').childNodes[0].src = './img/sn_30.jpg';
		} ;
	}
}