A while back Robert Douglass had written a great guide to setting up Acquia Dev Desktop to use Xdebug on Mac OS X. Looking for it today it looks like the sands of time have erased it from the webs. At the same time the recent versions of Dev Desktop include Xdebug so the process is a little different (and simpler).
In this case I'm setting up Xdebug to work with Komodo IDE and Dev Desktop that comes bundled with Drupal 7. After installing Dev Desktop and setting up your first site it's time to enable Xdebug. In the recent versions of Dev Desktop it ships with Xdebug but the PHP extension is turned off.
The first step is launching the Dev Desktop control panel. Once it has started click the "Settings..." button in the lower right. Then pick the "Config" tab at the top center to see the server configuration. The screen shot here shows PHP 5.2 but the process is the same for 5.2 or 5.3. Whichever version of PHP click the Edit link beside the php configuration files.
This will open the chosen php.ini file in Text Edit. With the file open look for the line containing xdebug.so. If the installation is in the standard directory it will look something like this: