Grazie 
Questo il codice di index.php (è praticamente tutto HTML)
Codice PHP:
<?php
session_start();
?>
<html>
<head>
...
</head>
<body lang="it-IT" text="#000000" dir="ltr" style="background: transparent">
<center>
<table width="500" cellpadding="4" cellspacing="0"><col width="281">
<tr>
<td width="281" valign="top" style="border: 1px solid #000080; padding: 0.1cm">
<form action="home.php" method="POST">
<p align="center">
<font face="DejaVu Sans, sans-serif">Nome utente: <INPUT TYPE = "Text" NAME = "username" maxlength="15">
</p>
<p align="center" style="font-style: normal; font-weight: normal">
<font face="DejaVu Sans, sans-serif"><center>Password: <input type="password" name="password"/> </font></center>
<br><center><input type="submit" value="Entra" name="entra" /></center>
</form>
</p>
</td>
</tr>
</table>
</center>
</body>
</html>
Questo invece il codice di home.php:
Codice PHP:
<?php
session_start();
$PHPSESSID=session_id();
?>
<html>
<style type="text/css">
(un po' di CSS incorporato)
</style>
<head>
<?php
$conn=mysql_connect("localhost", "...", "...");
$db=mysql_select_db('...', $conn);
$sezione=$_GET["m"];
?>
</head>
<body>
<br>
<span style="font-family: Helvetica,Arial,sans-serif;">
<?php
//acquisizione dati login
$user = $_POST["username"];
$pass = $_POST["password"];
?>
---qui vengono generati link (corretti) del tipo home.php?m=value---
</body>
</html>