Entirely reinventing the wheel seems foolhardy, and so I wanted to base the project on a solid foundation, including a quality PHP-based Twitter library. That library turned out to be PEAR's Services_Twitter package. In this article I'll introduce you to this powerful package, which although still in beta already offers all of the features you'll need whether you want to build your own Twitter client or simply add Twitter-specific functionality to an existing application.
He includes instructions on how to install the package, register the application as a service and connect it via OAuth. There's also a full code listing included showing how to make the authentication from the PHP app and how to grab the latest tweets from a user.