Specified module cannot be loaded error for PHP when start Apache

I am trying to enable extensions in PHP5 and integrate it with Apache2 web server on Windows XP, but I get the following error: PHP Startup: Unable to load dynamic library 'E:\PHP\ext\php_mysql.dll' - the specified module could not be found. The php_mysql.dll file exists in E:\PHP\ext and the permissions are set so it's readable, so that's not the problem. I've checked in my php.ini file which is in E:\php that the extension_dir = "E:\php\ext" and I've followed everything from http://ca3.php.net/manual/en/install.windows.manual.php. I added E:\php to my PATH and set the PHPIniDir directive as sepcified on the link. However, it still doesn't work. Anybody know what may be going wrong? Thanks. Alvin