php_pgsql.dll "Procedure could not be found"

Hi there. I'm running IIS version 4.0 and PHP verion 4.0 under WinNT 4.0. I am attempting to use the php_pgsql.dll extention library. This file is located in the same directory as all the other php_*.dll files, and the extention=php_pgsql.dll line in php.ini has been un-commented. When I load a php script into my browser, I'm greeted with a pop-up box which says "Unable to load dynamic library 'php_pgsql.dll' - The specified procedure could not be found" Note that if I remove a different library I'm also using from that directory, the error message I receive says "... specified *module* could not be found" rather than procedure. I frankly have no idea what this means, or why I'm having any difficulty loading this library with my php script. Any help is thoroughly appreciated. Thank you, Paul Lalli