Object Oriented Programming in PHP

Object Oriented Programming is the one area of PHP programming that I’m having difficulty grasping :(

I’ve managed to come to terms with functions, regular expressions and the likes, but I just can’t seem to grasp the concept of methods, and especially stuff like passing by reference! Are there any tricks other programmers out there use?
If you know of any good books, articles or tutorials that might help me in my quest to overcome this affliction, please, please, let me know!