Consider the following from an httpd.conf file...
LoadModule php5_module "E:/xyz/php/php5apache2_2.dll"
...which led to the dreaded...
PHP Warning: PHP Startup: Unable to load dynamic library 'E:\\xyz\\php\\ext\\php_mysql.dll' - The specified module could not be found.
Note, however, that PHP.exe apparently was found and executed php pages in Apache, but the MySQL functions therein failed.
Because PHP dir was not in $PATH, php5apache2_2.dll failed to find php_mysql.dll (the only extension I enabled) during Apache 2.2 start.
== Caveat (!)
The BIG issue is that, setting $PATH in...
<desk icon>My Computer
...didn't export the $PATH change such that restarting the Apache service (in MMC) would pick it up. So I tested the working solution (adding PHP dir to $PATH), but it failed because of HOW I set it. It succeeded only when I REBOOTED after changing the $PATH. There may be an easier way that this, but I do not know it at present.
Consider whether PHP dir should need to be in $PATH at all, when PHP.exe apparently was found and executes php pages in Apache, but php5apache2_2.dll failed to find whatever was needed to load the extensions. This should perhaps be addressed.
Note that on a WAMP installation (W2K,Apache,MySQL,PHP), only PHP is required in $PATH.