BD,
I have used Macs, but not OS X and I have not installed Moodle on a Mac. I do know that OS X is a form of Unix or Linux and I have installed Moodle on Linux. More to the point, I know that you can find the location of your active php.ini file (you can have more than one in your file system but only one active php.ini) by running the phpinfo script. See http://docs.moodle.org/en/phpinfo. Its output tells you where your active php.ini file is. You might already have a phpinfo script in your Moodle (web) folder; if so, it is probably called phpinfo.php. If not, that would be the place to put it; you can call it what you want (as long as it isn't the same name as an existing file), but it must end ".php". Then run it by pointing your browser to it.
Look for "Configuration File (php.ini) Path" on the left side near the top of the output.
RLE