function displaySub(id) {
	var imgName;
	var re;
	for(i=1 ; i<=8 ; i++) {
		document.getElementById("main_menu_sub"+i).style.display="none";
		imgName = document.getElementById("subMenuImg_"+i).src;
		re = /on\./g;
		document.getElementById("subMenuImg_"+i).src = imgName.replace(re,"off.");		
	}
	if(document.getElementById("main_menu_sub"+id)){
		document.getElementById("main_menu_sub"+id).style.display="block";
		imgName = document.getElementById("subMenuImg_"+id).src;
		re = /off\./g;
		document.getElementById("subMenuImg_"+id).src = imgName.replace(re,"on.");	
	}
}