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the login script:

<?php
$host="localhost"; // Host name
$username=""; // Mysql username
$password=""; // Mysql password
$db_name=""; // Database name
$tbl_name="members"; // Table name

// Connect to server and select databse.
mysql_connect("$host", "$username", "$password")or die("cannot connect");
mysql_select_db("$db_name")or die("cannot select DB");

// username and password sent from form
$myusername=$_POST['myusername'];
$mypassword=$_POST['mypassword'];

// To protect MySQL injection (more detail about MySQL injection)
$myusername = stripslashes($myusername);
$mypassword = stripslashes($mypassword);
$myusername = mysql_real_escape_string($myusername);
$mypassword = mysql_real_escape_string($mypassword);

$sql="SELECT * FROM $tbl_name WHERE username='$myusername' and password='$mypassword'";
$result=mysql_query($sql);

// Mysql_num_row is counting table row
$count=mysql_num_rows($result);
// If result matched $myusername and $mypassword, table row must be 1 row


if($count){
            session_start();
           session_regenerate_id();
            $_SESSION['SESS_USERNAME'] = $myusername;
            $_SESSION['SESS_PASSWORD'] = $mypassword;
            session_write_close();
           header("location: login_success.php");
}

       else
        {
         echo"<html>
        <head>
        <link href='styles.css' rel='stylesheet' type='text/css'/>
        </head>
        <body>
        <div id='main'>
        <div id='header'>
        </div>
        <div id='contentWrapper'>
        <div id='leftBox'>
        <div id='leftBoxContent'>
        <div id='lightBox'>
         </div>
        </div>
       </div>
       <div id='rightBox'>
    </div>
       <div id='content'>
        <p>Wrong Username or Bad Password.</p>
        <p><a href='./index.php'>Click Here</a> to try again.</p>
    </div>
    <br class='clearFloat'/>
  </div>
  <div id='footer'></div>
</div>
        </body>
        </html>";
        }
?>

check login script:

<?php
session_start();
if(!isset($_SESSION['SESS_USERNAME']) || !isset($_SESSION['SESS_PASSWORD']) || (trim($_SESSION['SESS_USERNAME']) == '')) {
                //someone's not logged in
        header("location: index.php"); //it's suppose to actually be there
                exit();
}
?>

and whats on top of every page:

<?php
require_once("checklogin.php");
?>