I wanted to modify it so that not only the very latest news can be printed, but all since the last printed to channel.

I have two columns on using RSS and showing only "what's new". There's the classic column that sends email, and the modern version that uses POE and Perl/Tk. Check both of them for how to handle seeing only "what's new". In fact, the POE-based version would turn into a great bot if you add POE::Component::IRC.