New on the Developer Tutorials site there's a tutorial from Padraic Brady showing how to create a simple Twitter client (to connect and send a tweet to the timeline) via an OAuth (Zend_OAuth) connection.

I finally got around to patching and finishing Zend_Oauth's Consumer implementation for the OAuth Core 1.0 Revision A specification. Once I had it finished, I used it to write a quick and simple interface to post some Tweets on Twitter while I was testing it out. [...] In this article I'll explore how to writea quick Twitter client so you can post tweets (those short messages of less than 140 characters) once authorised across the OAuth protocol.

He briefly covers what OAuth is and how its used to connect to sites in place of the more widespred method of a username/password combination. His script shows how to create the OAuth object with the right credentials and have it send a tweet as that login.