Loading DLL Extension

I can't seem to be able to load any of the DLL extensions included with PHP. For example when I try to load the pdf extension using: dl("php_zlib.dll"); or displaying phpinfo() I get this message in a warning window: pdf: Unable to initialize module Module compiled with debug=o, thread-safety=1 module API=20000809 PHP compiled with debug=o, thread-safety=1 module API=20001222 These options need to match I am running: WINNT 4.0 SP 6a Apache 1.3.12 PHP 4.0.6 php.ini settings: extension_dir = j:\php\extensions enable_dl = On extension=php_pdf.dll Any thoughts? Thanks. Zach Curtis POPULUS