[assassingod]

PHP Code:

        mysql_query("update user set tos = 'y' where id='$user[userid]'"); 


That should be

PHP Code:

        mysql_query("update user set tos = 'y' where userid='$user[userid]'"); 


The column is called userid, not id

Also, you can require global.php and you wont have to use mysql_query:

PHP Code:

<?php

require_once('./global.php');

if ($_POST['agree'] == 'y')
{
echo $user[userid];
        $DB_site->query("update user set tos = 'y' where userid='$user[userid]'");
        echo 'redirect code';
}
?>