function validateForm(form) {
  var warn = "";

  if (form.first_name.value == '') {
    warn += "First Name is required\n";
  }
  if (form.last_name.value == '') {
    warn += "Last Name is required\n";
  }
  if (form.email.value == '') {
    warn += "Email address is required\n";
  }

  if(warn != "") {
    alert(warn);
    return false;
  } else {
    return true;
  }

}