Being a Microsoft / Unix web developer, I’ve had a learning curve to overcome with running Apache / PHP / MySQL on OS X. Its actually extremely easy, but there are a few gotchas. These articles from Mac Dev Center were extremely helpful….
Apache Web-Serving with Mac OS X: Part 1
Apache Web-Serving with Mac OS X: Part 2
Apache Web-Serving with Mac OS X: Part 3
Apache Web-Serving with Mac OS X: Part 4
Apache Web-Serving with Mac OS X: Part 5
Apache Web-Serving with Mac OS X: Part 6