function do_check() {

  if (document.Formular.Versender.value == "") {
    alert("Please enter your name...");
    document.Formular.Versender.focus();
    return false;
  }

  if (document.Formular.Betreff.value == "No subject") {
    alert("Please select a subject...");
    document.Formular.Betreff.focus();
    return false;
  }

  if (document.Formular.Nachricht.value == "" || document.Formular.Nachricht.value == "Your message") {
    alert("Please enter a message...");
    document.Formular.Nachricht.focus();
    return false;
  }

}