Newbie - Help with WAMP

Hi, I am running PHP 5, MySQL 4.1 and Apache 2.0 on an XP Pro Box. I would like MySQL to serve HTTP pages via PHP. After configuring the setup, on restarting Apache, I receive a 'php_mysql.dll file cannot be found' error message. However, the webserver starts but, of course, I cannot access MySQL. The .dll is in the 'ext' folder and this is correctly named in the php.ini file. I can see the file, and I have checked the wording to make sure I have no typos. This is driving me barmy - could someone give a bit of advice please to get me out of this one? Cheers, Mike