The vast, vast majority of web hosts have not implemented php5 - it's too new, and still use php4. The vast majority of the functions in php4 are present in php5. So there is no reason to throw the book away. For example, I learned VB for a college course from a VB4 textbook, and never found anything it said no longer applied. (I learned php basics from a php3 textbook, and have only discarded one thing that was used in php3 and is no longer needed)

Recently I've used the book Web database applications with php and mysql, by Williams and Lane, and it was pretty reasonable. Certainly the secure log in system I copied from it worked okay and the client was happy with it.