I haven't done any work in PHP5, but I earn my living in PHP4, including some hairy OO stuff at the limits of the language.

You can get a lot done staying almost completely away from objects. I've seen three whole website infrastructures - all completely different - using only functions, or objects in a very simple sense. It's really only when you get into the quirks of references that you will have issues between 4 and 5, but if you don't know what they are, then you'll be fine for quite a while. The language masters spent a lot of time trying to avoid surprises for those moving lots of existing code from 4 to 5.

And whatever structure you create to look after things for you, be prepared to rewrite it eventually - perhaps twice - when you have more experience at creating that sort of thing. That doesn't include wholesale changes before you get the first one working. :-)

Wade.