On PHPFreaks.com there's a new tutorial providing a beginner's guide to debugging in PHP (with the built in functionality PHP has, not external software).

Everyday the forums see probably hundreds of topics posted where the problem is a fairly simple error. [...] As a beginner, it can be difficult to find and solve these errors. By tackling each of these in turn, I hope to teach you some methods of finding and solving them.

They look at the different sorts of errors - syntax errors, fatal errors, warnings, notices - as well as some of the ones a bit harder to track down like database problems and logical errors.

On his blog, Justin has posted an article from David Sklar today - a look at PHP error reporting - conifguration, locating errors, and checking variable values as the script runs.

Whether you're a PHP newbie or a wizard, your programs are going to have bugs in them. Nobody's perfect.

This article gives you some techniques for finding and fixing the problems in your programs. It covers three topics: how to get the PHP interpreter to report the errors that interest you, how to locate basic syntax errors in your program, How to check the values of variables as your program is running.

The configuration section mentions the display_errors and log_errors options to help debug your scripts. There's also a bit describing what the different error types mean (parse, fatal, strict) and simple things to look for to handle them. He also suggests some other resources to look at to help with more detailed error reporting...