<?php
//.....
$insert_sql = "INSERT INTO users (first_name, last_name, email, bio, facebook_url, twitter_handle) " .
"VALUES ('{$first_name}', '{$last_name}', '{$email}', '{$bio}', " .
"'{$facebook_url}', '{$twitter_handle}');";
// Insert the user into the database
mysql_query($insert_sql);
var_dump(mysql_insert_id());//COSA DA?
//la riga sotto provvisoriamente la commenti per vedere il var_dump
//header("Location: show_user.php?user_id=" . mysql_insert_id());
?>