Go to http://www.zend.com/en/community/pdt#debugger and download Eclipse PDT All-in-one. I picked the Linux 32 bit version for installation in Ubuntu.

Unpack the downloaded file (zend-eclipse-php-helios-linux-gtk-x86.tar.gz).

Execute the eclipse/eclipse executable to launch Eclipse, and pick the appropriate workspace.

Create a new PHP project (File > New) and ensure that its location is in the same area that is monitored by your Apache install. In my case, this is /home/damodar/public_html, so my “test” project is located at /home/damodar/public_html/test.

Create a new PHP file.

Debug as PHP Script, if you want to run it locally in a PHP interpreter within the PDT.

Debug as PHP Web Page, if you want to run it in a browser.

You can place breakpoints as appropriate.

Enjoy!

(Thank you Zend Technologies, for making this so easy!)

Note: You can also use the Zend Server Community Edition as your web server. As noted, I chose to stay with Apache instead.