Si l'ho usato, ma come faccio a richiamarlo sull'altra pagina?

Comunque ecco a te il codice se vuoi dargli un occhiata
codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
 "http://www.w3.org/TR/html4/loose.dtd">
<?
session_start(); 
include("config-riservato.php"); 
?>
<html>
  <head>
    <title>Login Pannello</title>
  </head>
  <body>
    <center>
      <div style="backcolor: #ffffff">
        <center>
          [img]Immagine.PNG[/img]
        </center>
      </div>
      <table border="0" width="474" background="sfumaomogeneasb1.jpg" height="234">
        <tbody>
          <tr>
            <td>

            <center>
              Per favore, inserisci i tuoi dati per effettuare l'accesso. 
            </center>
            <?
function check($username,$password){
		$username = addslashes($username);
		$password = addslashes(md5($password));
		
		connetti();
		$r = mysql_query("SELECT * FROM pannellomod WHERE username = '$username' AND password = '$password'");
		$n = mysql_num_rows($r);
		if (!($n)){
			return false;
		}else{	
			return true;
		}
}

function form_login(){
?>
            <form id="login" method="post" action="<?=$PHP_SELF?>">
              <div style="TEXT-ALIGN: center; MARGIN-LEFT: auto; MARGIN-RIGHT: auto">
                
Username: <input maxlength="255" name="username">
Password:<input maxlength="255" type="password" name="password">

<input value="Accedi" type="submit" name="OK">
              </div>
            </form>
            <? }

if(isset($_POST["username"])){
	if (check($_POST["username"],$_POST["password"])){
		$_SESSION["username"] = $_POST["username"];
		$_SESSION["password"] = $_POST["password"];		
echo "<p align='center'> Hai appena effettuato l'accesso!
Accedi al pannello || Disconnetti</p>";
header("location: http://wikiforix.lwsserver.com/mod-pannel/pannello.php");

	}else{
		form_login();
	}
}else{
	form_login();
}		
?>
            </td>
          </tr>
        </tbody>
      </table>
      <div>
         
      </div>
      <div>
         
      </div>
      <div>
         
      </div>
      <div>
         
      </div>
    </center>
    <div align="center">
      <hr style="WIDTH: 79.42%; HEIGHT: 1px" color="#000000" size="0" width="79.42%">
    </div>
    <p align="center">Copyright &copy; 2010 <a href="mailto:luigi.parziale@live.it">Luigi
    Parziale (ixol)</a></p>
  </body>
</html>