From our sister site, AjaxDeveloper.org today, there's a new post with a pointer to this new tutorial over on PHPit.net that talks about the creation of a simple Ajax/PHP chat script.

In this first part of the series I will show you how to create a really basic chat script, and nothing more. In the next parts we'll be adding more features, eventually creating a really robust and powerful chat script.

He starts off by explaining how it will work from an overall perspective, illustrating the role each technology will play. From there, it's all about the code - first the server-side aspect of the script, then on to the client.