function layerVis(id,dir) {
    if (document.layers) {
        v = (dir == "on") ? "show" : "hide";
        //document.layers[id].visibility = v;
    }
    else if (document.all) {
        v = (dir == "on") ? 'visible'	: 'hidden';
        document.all[id].style.visibility = v;
    }
    else if (document.getElementById) {
        v = (dir == "on") ? 'visible' : 'hidden';
        document.getElementById(id).style.visibility = v;
    }
}
var lastClicked=null;

function clickOnOrOff(id,url){
	if(document.layers){
		if (lastClicked==null){
			layerVis(id,"on");
			lastClicked=id;
		}
		else if(id==lastClicked){
			layerVis(id,"off");
			lastClicked=null;
		}
		else{
			layerVis(lastClicked,"off");
			layerVis(id,"on");
			lastClicked=id;
		}
	}
	else{
		document.location=url;
	}

}

function popUp(URL) {
day = new Date();
id = day.getTime();
eval("page" + id + " = window.open(URL, '" + id + "', 'toolbar=0,scrollbars=0,location=0,statusbar=0,menubar=0,resizable=0,width=450,height=200,left = 415,top = 412');");
}

<!--
var timeout         = 500;
var closetimer		= 0;
var ddmenuitem      = 0;

// open hidden layer
function mopen(id)
{	
	// cancel close timer
	mcancelclosetime();

	// close old layer
	if(ddmenuitem) ddmenuitem.style.visibility = 'hidden';

	// get new layer and show it
	ddmenuitem = document.getElementById(id);
	ddmenuitem.style.visibility = 'visible';

}
// close showed layer
function mclose()
{
	if(ddmenuitem) ddmenuitem.style.visibility = 'hidden';
}

// go close timer
function mclosetime()
{
	closetimer = window.setTimeout(mclose, timeout);
}

// cancel close timer
function mcancelclosetime()
{
	if(closetimer)
	{
		window.clearTimeout(closetimer);
		closetimer = null;
	}
}

// close layer when click-out
document.onclick = mclose; 
// -->