And the relevant bit from the php.ini
==================================
; Directory in which the loadable extensions (modules) reside.
extension_dir = ".;C:\PHP\extensions;"
==================================
You need extension_dir to point to the location where your extensions are located. Just set the absolute path in your php.ini:
extension_dir = "c:\php\extensions"
Also is the library actually IN your extensions directory? I'm not running php 4 or else I could give more precise answers... sorry!