On PHPBuilder.com today there's a new tutorial from Vojislav Janjic about using a simple DOM parser in PHP to edit the markup even if it's not correctly W3C-formatted - the Simple HTML DOM Parser

Simple HTML DOM parser is a PHP 5+ class which helps you manipulate HTML elements. The class is not limited to valid HTML; it can also work with HTML code that did not pass W3C validation. Document objects can be found using selectors, similar to those in jQuery. You can find elements by ids, classes, tags, and much more. DOM elements can also be added, deleted or altered.

They help you get started using the parser, passing in the HTML content to be handled (either directly via a string or loading a file) and locating elements in the document either by ID, class or tag. Selectors similar to those in CSS are available. Finally, they show how to find an object and update its contents, either by adding more HTML inside or by appending a new object after it.