You can check if the ldap extension is in use after copying the above file and when Apache finally starts by going tohttp://localhost/xampp/phpinfo.php
Look for the ldap section which should indicate enabled.
If Apache is running as a Windows service then, as you say, a reboot may have the newly copied file recognised.
Also if you have ldap issues then this site might be worth a visit:http://www.cyrusimap.org
BTW. XAMPP in a production environment is not recommended because of the open security issues - keep a close eye on your on your access.log file in the apache\logs folder.