The DeveloperTutorials website has a new tutorial posted today that covers their method for combining Ajax and PHP to create a custom form handler.

For this project, I needed a form to send an email to the client once it's been validated and checked to be ok. [...] I decided to spice things up a bit with a little AJAX and a few effects from Scriptaculous. So let's dive into exactly how I did it.

They create their form first - a standard user info type of thing - and set it up to use the WForms validation script in PHP. They include the Javascript the script needs to run the validation and to handle sending the form's contents back out via an email.