function click(e) {
  if (navigator.appName == 'Netscape'
           && e.which == 3) {
      alert("Sorry that is not allowed")
      return false;
      }
   else {
      if (navigator.appName == 'Microsoft Internet Explorer'
          && event.button==2)
         alert("Sorry that is not allowed")
         return false;
         }
   return true;
 }
document.onmousedown=click