You also have to tell PHP to load the extension. Check your
php.ini file for this line:
... if it's there, remove the leading semi-colon
; and restart your web server. If it's not there, just add it.
As for the extension directory, mine is specified at line 461. Make sure yours is really not there before you add it yourself. Because if you ad yours before the one that's already there, it'll just be overwritten.
It's very important that you restart your web server after making changes in
php.ini, 'cause they won't take effect otherwise.