Form Validation

[beav33 0]

This is some of the code below that dreamweaver places for a registration record set. Now I want to validate some things like making sure the passwords match up and email, so on. I can't figure out how to change my code to identify it. My code is below dreamweavers, please help.

// *** Redirect if username exists
$MM_flag="MM_insert";
if (isset($_POST[$MM_flag])) {
  $MM_dupKeyRedirect="takenusername.php";
  $loginUsername = $_POST['username'];
  $LoginRS__query = sprintf("SELECT username FROM register WHERE username=%s", GetSQLValueString($loginUsername, "text"));
  mysql_select_db($database_db_connect, $db_connect);
  $LoginRS=mysql_query($LoginRS__query, $db_connect) or die(mysql_error());
  $loginFoundUser = mysql_num_rows($LoginRS);

  //if there is a row in the database, the username was found - can not add the requested username
  if($loginFoundUser){
    $MM_qsChar = "?";
    //append the username to the redirect page
    if (substr_count($MM_dupKeyRedirect,"?") >=1) $MM_qsChar = "&";
    $MM_dupKeyRedirect = $MM_dupKeyRedirect . $MM_qsChar ."requsername=".$loginUsername;
    header ("Location: $MM_dupKeyRedirect");
    exit;
  }
}

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

if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "form1")) {
  $insertSQL = sprintf("INSERT INTO register (username, password, email, companyname, firstname, lastname, phone) VALUES (%s, %s, %s, %s, %s, %s, %s)",
                      GetSQLValueString($_POST['username'], "text"),
                      GetSQLValueString($_POST['password'], "text"),
                      GetSQLValueString($_POST['email'], "text"),
                      GetSQLValueString($_POST['companyname'], "text"),
                      GetSQLValueString($_POST['firstname'], "text"),
                      GetSQLValueString($_POST['lastname'], "text"),
                      GetSQLValueString($_POST['phone'], "text"));

Dreamweaver's way to check username and varibles.
My code
  //create short variable names
  $email=$_POST['email'];
  $username=$_POST['username'];
  $password=$_POST['password'];
  $password2=$_POST['password2'];
  $companyname=$_POST['companyname'];
  $firstname=$_POST['firstname'];
  $lastname=$_POST['lastname'];
  $phone=$_POST['phone'];

Then on down the validation

    // passwords not the same
    if ($password != $password2)
    {
      throw new Exception('The passwords you entered do not match - please go back'
                          .' and try again.');

Just need to change it up a bit to work with dreamweaver's code. BUT HOW?
Thank you,
beav33