The first step would be to create a special user that only had access to the one table. I'm not sure if that would be enough to hide the other tables (they might still be able to see them, even if they can't interact with them). The second step would be to edit "includes/class/Sql.php" or "includes/class/Sql-php4.php" depending on which version of php you are running. Now I assume you are running mysql and not sqlite. Next you would look for a function in that file called listTables(). You would edit this line:
return $this->query("SHOW TABLES");
to look something like this:
return $this->query("SHOW TABLES LIKE 'helpdesk'");
This solution may or may not work, you will have to test it yourself.
Calvin