On the NETTUTS.com site today there's a new tutorial by Steve Guidetti about understanding and handling polymorphism in PHP - making interfaces to multiple objects that all work the same way. In this tutorial he gets more in depth and includes some code to illustrate.

In object oriented programming, polymorphism is a powerful and fundamental tool. It can be used to create a more organic flow in your application. This tutorial will describe the general concept of polymorphism, and how it can easily be deployed in PHP.

He explains to concept of polymorphism for those that haven't seen it before - common interfaces to multiple objects - and how to can help make using the parts of your application much simpler. In his code examples he uses interfaces and abstract classes to make the connections. The interfaces define the structure to follow and the abstract classes are the multiple objects that must follow it.