On SmashingMagazine.com they've posted a great PHP tutorial that walks you through the full process of what you need to know to really get started with the language.

In this article, I'll introduce you to the fundamentals of PHP. We'll focus on using PHP to access Web services and on turning static HTML pages into dynamic ones by retrieving data from the Web and by showing different content depending on what the user has entered in a form or requested in the URL. You won't come out a professional PHP developer, but you'll be well on your way to building a small page that uses Web services.

They help you set up either MAMP of XAMPP and all of the basics to introduce you to the language:

• Variable types (simple and complex)
• Conditionals
• Functions
• Superglobals
• Pulling data from remote sources