I have a couple of dedicated Mac OS X Servers running all of my websites, including my XF forums. It is very simple if you install Server.app from the Mac App Store, this will give you most of the services needed (Apache 2.2.xx and PHP 5.3.xx, along with DNS, FTP and Mail). I prefer this slightly over the combined packages that are out there.
The only thing you need to install from there is MySQL, as PostgreSQL is the default DBMS on Mac OS. There is a DMG which is easy to install for MySQL, including a service to auto-start the instance.
Let me know if you run into any issues or have questions.