When using PHP 5.2.0 within WinXP via Wampserver ( http://www.en.wampserver.com/download.php ) you will find that just simply adding a PECL-based DLL file into php.ini is not enough. Steps you will have to do to ensure that your PECL extension(s) will be recognized are as follows:
1) Have the DLL referenced within PHP's php.ini ("extension=[php_name-of-PECL-extension].dll")
2) Have the DLL referenced within Windows' php.ini
3) Have the DLL within wampserver.ini
If any of these steps are not included, alongside the obvious web services restart, then PECL is not recognized.