WinXP SP3, PHP 5.2.17, Apache 2.2

I am running Windows XP with Apache Server and PHP.
Attempting to use Firebird/Interbase module.
<?php phpinfo(); ?> works fine.

The loaded configuration file is C:\php\php.ini

The problem is when I uncomment the following
;[PHP_INTERBASE]
;extension=php_interbase.dll

and then reload Apache, it fails to load because it says it can't find
C:\php\ext\php_interbase.dll

But the file is there.

The other modules load fine and they are in the same folder:
[PHP_MYSQL]
extension=php_mysql.dll
[PHP_PDO]
extension=php_pdo.dll
[PHP_PDO_MYSQL]
extension=php_pdo_mysql.dll
[PHP_PDO_ODBC]
extension=php_pdo_odbc.dll
[PHP_PDO_SQLITE]
extension=php_pdo_sqlite.dll
[PHP_SOCKETS]
extension=php_sockets.dll
[PHP_XMLRPC]
extension=php_xmlrpc.dll
;[PHP_INTERBASE]
;extension=php_interbase.dll

So now I cannot use a Firebird database. Any ideas?
john c.