From Carlo on the FCHouse.com blog, there's this new guide to debugging your PHP5 application with the Eclipse PDT functionality in an OS X environment.

In these months I have developed in PHP with Eclipse PDT (Php Development Tool). During the first days I tried to make the debugging works, but without great results, therefore I dropped and I took back the usual debugging technique of every good script developer: echo $variableName; or simply logging everything possible in some log files.

Knowing that this wasn't "the right way" to do things, Carlo searched for something better. He found a hint on another blog and ultimately figured out how to get his Eclipse/Apache/XDebug installation to work on his Mac. His post also includes the "glue" that you'll need to get them all working happily together.