Ayuda con Login Ya Creado En Dreamweaver

[xxrandyxx]

Pero en donde pongo

session_start();
session_destroy();
session_unset();

en el link ?

este es mi php

<?php require_once('Connections/resiper_bd.php'); ?>
<?php
//initialize the session
if (!isset($_SESSION)) {
session_start();
}

// ** Logout the current user. **
$logoutAction = $_SERVER['PHP_SELF']."?doLogout=true";
if ((isset($_SERVER['QUERY_STRING'])) && ($_SERVER['QUERY_STRING'] != "")){
$logoutAction .="&". htmlentities($_SERVER['QUERY_STRING']);
}

if ((isset($_GET['doLogout'])) &&($_GET['doLogout']=="true")){
//to fully log out a visitor we need to clear the session varialbles
$_SESSION['MM_Username'] = NULL;
$_SESSION['MM_UserGroup'] = NULL;
$_SESSION['PrevUrl'] = NULL;
unset($_SESSION['MM_Username']);
unset($_SESSION['MM_UserGroup']);
unset($_SESSION['PrevUrl']);

$logoutGoTo = "home.php";
if ($logoutGoTo) {
header("Location: $logoutGoTo");
exit;
}
}
?>
<?php
if (!function_exists("GetSQLValueString")) {
function GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "")
{
$theValue = get_magic_quotes_gpc() ? stripslashes($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;
}
}

mysql_select_db($database_resiper_bd, $resiper_bd);
$query_rslogueo = "SELECT * FROM usuario ORDER BY nombre ASC";
$rslogueo = mysql_query($query_rslogueo, $resiper_bd) or die(mysql_error());
$row_rslogueo = mysql_fetch_assoc($rslogueo);
$totalRows_rslogueo = mysql_num_rows($rslogueo);
?>
<?php
// *** Validate request to login to this site.
if (!isset($_SESSION)) {
session_start();
}

$loginFormAction = $_SERVER['PHP_SELF'];
if (isset($_GET['accesscheck'])) {
$_SESSION['PrevUrl'] = $_GET['accesscheck'];
}

if (isset($_POST['textfield'])) {
$loginUsername=$_POST['textfield'];
$password=$_POST['textfield2'];
$MM_fldUserAuthorization = "";
$MM_redirectLoginSuccess = "usuario.php";
$MM_redirectLoginFailed = "error.php";
$MM_redirecttoReferrer = true;
mysql_select_db($database_resiper_bd, $resiper_bd);

$LoginRS__query=sprintf("SELECT email, clave FROM usuario WHERE email=%s AND clave=%s",
GetSQLValueString($loginUsername, "text"), GetSQLValueString($password, "text"));

$LoginRS = mysql_query($LoginRS__query, $resiper_bd) or die(mysql_error());
$loginFoundUser = mysql_num_rows($LoginRS);
if ($loginFoundUser) {
$loginStrGroup = "";

//declare two session variables and assign them
$_SESSION['MM_Username'] = $loginUsername;
$_SESSION['MM_UserGroup'] = $loginStrGroup;

if (isset($_SESSION['PrevUrl']) && true) {
$MM_redirectLoginSuccess = $_SESSION['PrevUrl'];
}
header("Location: " . $MM_redirectLoginSuccess );
}
else {
header("Location: ". $MM_redirectLoginFailed );
}
}
?>

que estoy haciendo mal ? :(