proses_login.php nya,,
<?php
    include "config.php";
    $username = $_POST['username'];
    $password = $_POST['password'];

    $login = mysql_query("SELECT * FROM tab_user WHERE username='$username' AND password='$password'");
    $hasil = mysql_num_rows($login);
    $r = mysql_fetch_array($login);

    if ($hasil > 0)
    {
      session_start();
      session_register("user_id");
      session_register("username");
      session_register("password");
      session_register("user_akses");
      $_SESSION[user_id]     = $r[user_id];
      $_SESSION[username]     = $r[username];
      $_SESSION[password]     = $r[password];
      $_SESSION[user_akses]    = $r[user_akses];
      header('location:index.php');
    }
    else{ echo "LOGIN GAGAL! <br> <a href='index.php'><< Kembali</a>"; }
    ?>