PHP & MySQL for dummies. Don't be put off by the name it's a brilliant book.
To be honest actually I taught myself. Downloaded source codes for existing websites and played around with them until they did what I want. You can learn a surprising about that way. Any time I got stuck I would ask a question on phpfreaks (google it, I forget the exact address) or look it up in the book (the Dummies one). Best combination I think is that book and a little exploration of your own.