To locate the ini file on your machine, open Terminal.app and run the following command:
Terminal.app
php --ini
If you need a template for Lion, try this.
You should find it in /private/etc if it exists, otherwise:
sudo cp /private/etc/php.ini.default /private/etc/php.ini
In terminal do php -i | grep php.ini.Should give you some clues ;)
php -i | grep php.ini