var popup=null;
function popupwindow(which,width,height)
{
	if(!width)
	{
		width=400;
		height=250;
	}

	if(popup!=null)
		popup.close();

	popup=window.open(which,'popup_window','toolbar=no,location=no,directories=no,status=no,scrollbars,resizable=yes,copyhistory=no,width='+ width+ ',height='+height);
}