Follow these steps to set up Eclipse as a full-featured PHP development environment, complete with debugging features.

1. If you don’t have Eclipse already installed, download it from this download page. Eclipse comes in lots of different flavors, for this tutorial you can choose Eclipse Classic. On Mac OS X, just drag the entire eclipse folder into your Applications folder.
2. We are now going to install some necessary plugins. From the menu, choose Help > Install New Software… .
3. A new window named “Install” has appeared. From the “Work with:” drop down menu choose All Available Sites. In the type filter text textbox right below, type PDT. Wait for some seconds for the list of available plugins to be populated. Then, expand the General Purpose Tools group, and tick PHP Development Tools (PST) SDK Feature. The window will now look like this:
   

   The "Install Software" window from Eclipse.

4. Press Next two times, accept the terms of the license agreements by clicking the appropriate radio button on the lower left corner, then press Finish. Then, restart Eclipse by choosing Restart Now.
5. We will now install the Zend PHP Debugger. Download the zip package from this link, and unpack it. The unpacked archive will contain two folders, named features and plugins.
6. Copy the contents of the features folder you unpacked in the features folder of your Eclipse installation (on your Mac, this will likely be /Applications/eclipse/features).
7. In the plugin folder, you will have 4 files. Copy both org.zend.php.debug.debugger_5.2.15.v20081217 and org.zend.php.debug.debugger.<YOUR_OS>_5.2.15.v20081217 in the plugins folder of your eclipse installation (again, on your Mac, this will likely be /Applications/eclipse/plugins) where YOUR_OS is the operating system you are using (Mac, Linux or Windows).
8. Restart Eclipse.

Please note that the Zend Debugger could also be installed using the Install Software window used in steps 2 and 3, but as of today the repository is broken. This is why we copied the files manually in steps 6 and 7. For more information visit the ZEND website, from which we retrieved the link used at Step 5.