The NetBeans people say that I need a Java Development Kit (JDK) 5 or 6 when I want to develop PHP with NetBeans on the Mac...
see: "To complete this tutorial, you need the following software and resources."
Now that sounds very strange to me. Must I really get that and spend some hours installing it? Why? What does Java have to do with PHP? Why's that a prerequisite?
NetBeans is written in Java, so...
The NetBeans IDE is written in Java and runs everywhere where a JVM is installed, including Windows, Mac OS, Linux, and Solaris. A JDK is required for Java development functionality, the PHP bundle can be used with just the JVM.
Netbeans is a Java application. I would expect at least a Java Runtime Environment. It may be possible to run it without the development kit if you're not developing Java. But if you have to download the JRE, you may as well get the JDK to be fully compatible.