I think you should download the new version of PHP you want to install, save you actual php.ini in a safe place and reinstall PHP. That's quite an easy thing to do on Win32. Only change (on httpd.conf), the lines refering to php, and in the new php.ini, load the modules you used to do.
Oh! And, if you aren't used to $GET, $POST, and such, put register_globals to on.
Hope this helps
fLIPIS