This might be due to different versions of the CGI and the DLL OR due to a misconfigured extensions directory in the PHP.ini file..
- Different Versions ------
Once you use the installer to install, take the ZIP version and basically replace the installed files with the ZIP files
php.exe
php4ts.dll
*.dll (the extensions)
If you've changed your .INI file, do not replace that with the ZIP'd version as you'll lose all your changes..
- Extensions Path --------
Basically look for the line that reads "extension_dir" and replace that with the path to your extensions:
ie. c:\php\extensions\
Have fun and good luck =)