On the Zend Developer Zone today, Vikram Vaswani has a tutorial posted introducing the PEAR HTML_QuickForm package and how to use validation right along with it.
Over the next few pages, I'll be introducing you to one of PEAR's most powerful tools for generating Web forms and validating the input that arrives through them: the HTML_QuickForm package. This package provides a flexible, reusable library of methods that can literally save you hours of time when dealing with form-based user input - and best of all, it's free and extremely easy to use. So what are you waiting for? Jump right in, and let's get going!
You'll need to be familiar with some of the technologies before getting started (it's not going to teach you PHP) and you'll need to have the software setup and ready with the HTML_QuickForm package installed. There's lots of different examples of form creation (including generated from database information) as well as information on the rules you can apply to your form elements to check on the user input (like alphanumeric, maximum length and matching a regular expression).