If you're running the ISAPI, you'll have a line like this in your httpd.conf, if you're using Apache:
LoadModule php4_module c:/php/sapi/php4apache.dll
If you're running CGI, you'll have something like this:
ScriptAlias /php/ "c:/php/"
AddType application/x-httpd-php .php
Action application/x-httpd-php "/php/php.exe"