If you are planning on implementing an interface to Arduino, consider using the firmware that I wrote for my Pd object. The intention is to be able to control as much as possible from the software on the host computer.
http://at.or.at/hans/pd/objects.html
The Plushie Message Framework is available to help you get started sending Internet data to Arduino. This uses PHP and has support for RSS and Adium chat, but can be extended for other uses. PMF was designed for DIY wireless toys.