function popup(myUrl,myName,mywidth,myheight)
{
  var winl = (screen.width - mywidth) / 2;
  var wint = (screen.height - myheight) / 2;
  var n=open(myUrl,myName,'toolbar=no,location=no,directories=no,status=no,menubar=no,titlebar=no,scrollbars=no,resizable=no,width='+mywidth+',height='+myheight+',left='+winl+',top='+wint+'');
  n.focus();
}