Hi Stu,
Since PHP isn't a strict OO language (it allows direct modification of class variables thus breaking encapsulation), it may be worthwhile learning OOP using Java first, and then when you have the grasp of this, you'll keep to the principles of OOP and not 'break' them using PHP.
http://sep.stanford.edu/sep/jon/family/jos/oop/oop1.htm
This tutorial is quite good and light hearted - although you may know all the stuff...
Anyway, I think OO basics first and then PHP specifics.