Chris Shiflett has a new post to his blog today about the new authentication model Twitter uses, OAuth, and how you can connect your PHP applications to their services.
I've been working on a project with my Analog friends that might use the Twitter API to streamline stuff like signup for those who already use Twitter. Because this now requires OAuth, I needed to implement OAuth quickly, so that we had something to test and consider.
He chose this Twitter library to connect his application and mentions the consumer key and consumer secret you'll nee to get from the Twitter development site. The library makes it as simple as passing these bits of information in and having the Twitter side handle it from there (a redirect to approval page). The callback URL is requested and you then have access to that user's information including name, location, URL and description.