function validEmail(email) {
  var needed=/^.+@.+\..{2,3}$/;
  if (!needed.test(email))
    return false;
  else
    return true;
}

function isZip (value) {
   var re = /^\d{5}([\-]\d{4})?$/;
   return (re.test(value));
}

function checkForm (f) {
  var result = true;
  var errors = "";

  if (!f.event_name.value) {
    errors += "Please enter an Event/Ad name.\n";
    result = false;
  }

  if (!f.event_info.value) {
    errors += "Please enter some information about this posting.\n";
    result = false;
  }

  if (!validEmail(f.contact_email.value)) {
    errors += "Please enter a valid email address.\n";
    result = false;
  }

  if (!isZip(f.contact_zip.value)) {
    errors += "Please enter a valid zip code.\n";
    result = false;
  }

  if (result == false) {
    alert(errors);
  }
  return result;
}