function display_sub_menu(which)
{
	document.getElementById('head_nav').style.height='1000px';
	document.getElementById('menu_'+which).style.visibility='visible';
	document.getElementById('menu_'+which).style.zIndex='999';
}

function hide_sub_menu(which)
{
	document.getElementById('head_nav').style.height='28px';
	document.getElementById('menu_'+which).style.visibility='hidden';
	document.getElementById('menu_'+which).style.zIndex='-1';
}