Want a free book on PHP 4.0? Simply click here for a free ebook on PHP 4.0 from Apress. It's not PHP 5.0 but hey it's free and lots of it will still be relevant. I found this through the Drupal Announcements RSS feed:
For the PHP 4.0 ebook, you should be able to simply go to http://apress.com/free/content/ProgrammersIntroductionToPHP4.pdf and view the PDF file. If that doesn't work, follow these steps:
1. Go to http://apress.com/free/index.html
2. Unclick “Subscribe to Apress newsletter” (unless you really want the newsletter).
3. Click “Download the book” without entering your email address (unless you want the newsletter).
4. On the next screen, to the right of where it says, “A Programmer's Introduction to PHP 4.0 (4.2 MB PDF file),” click on “Download now.”
5. The next screen takes you to http://apress.com/free/content/ProgrammersIntroductionToPHP4.pdf. It might take a few moments due to the PDF file being 4.2MB.