Can error messgaes be changed?

Re using e-mail as the primary key, this is a very basic application, we're trying to get an idea of how many people are likely to visit the airshow, how many cars or aircraft will have to be parked etc - it's totally unscientific but as this is the first airshow we've run it is better than anything else we have to gauge likely attendance. The e-mail address is there for two reasons:

1) We'd like to start building up a mail list for future airport promotions, there's an "opt-in" button following it

2) This will discourage some kid from entering the info multiple times as he'll have to enter different e-mail addresses each time.

Far from perfect I know, but probably adequate for our needs. I'll probably use the same approach for a feedback form that will be posted shortly and enabled immediately after the airshow.

Thanks

oops, sorry. I should also have mentioned that the web site is for an airshow (www.hollisterairshow.com) and the form is a planning form to help us gauge likely attendance and can be found here www.hollisterairshow.com/helpusplan.php

I'm using DW CS4 with a MySQL db.

The db is set up with the e-mail column defined as a Primary key and Unique, In DW I use the Insert Record behavior, here's the PHP code DW generates.

Thanks.

if (!function_exists("GetSQLValueString")) {
function GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "")
{
  if (PHP_VERSION < 6) {
    $theValue = get_magic_quotes_gpc() ? stripslashes($theValue) : $theValue;
  }

  $theValue = function_exists("mysql_real_escape_string") ? mysql_real_escape_string($theValue) : mysql_escape_string($theValue);

  switch ($theType) {
    case "text":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;   
    case "long":
    case "int":
      $theValue = ($theValue != "") ? intval($theValue) : "NULL";
      break;
    case "double":
      $theValue = ($theValue != "") ? doubleval($theValue) : "NULL";
      break;
    case "date":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;
    case "defined":
      $theValue = ($theValue != "") ? $theDefinedValue : $theNotDefinedValue;
      break;
  }
  return $theValue;
}
}

$editFormAction = $_SERVER['PHP_SELF'];
if (isset($_SERVER['QUERY_STRING'])) {
  $editFormAction .= "?" . htmlentities($_SERVER['QUERY_STRING']);
}

if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "form1")) {
  $insertSQL = sprintf("INSERT INTO plan (howArriving, howMany, Saturday, Sunday, camping, email, maillist, howHear) VALUES (%s, %s, %s, %s, %s, %s, %s, %s)",
                       GetSQLValueString($_POST['howarriving'], "text"),
                       GetSQLValueString($_POST['howMany'], "int"),
                       GetSQLValueString($_POST['whichdays'], "text"),
                       GetSQLValueString($_POST['whichdays'], "text"),
                       GetSQLValueString($_POST['RadioGroup1'], "text"),
                       GetSQLValueString($_POST['email'], "text"),
                       GetSQLValueString(isset($_POST['maillist']) ? "true" : "", "defined","'Y'","'N'"),
                       GetSQLValueString($_POST['howDidYouHear'], "text"));

  mysql_select_db($database_planconnection, $planconnection);
  $Result1 = mysql_query($insertSQL, $planconnection) or die(mysql_error());
}