I've been developing PHP on os X for about a year now, and I love it.
A few things:
-When you start web sharing, you are in fact starting APACHE- no need to install another version.
-PHP is installed but not configured with apache- you need to edit the apace config file. I suggest downloading BBEdit lite (it opens invisible files easily) to edit the config file.
-There is a 1 click install available for mySQL, but I don't remember where.
Best of luck