On PHPBuilder.com there's a new tutorial looking at using the SimplePie library to aggregate RSS feeds.

PHP developers are particularly lucky as a fantastic library named SimplePie not only offers the aforementioned features but also supports both RSS and Atom formats, multiple character encodings, and an architecture that makes integration with your favorite content management and blogging platforms a breeze. In this tutorial I'll introduce you to SimplePie, showing you how easy it is to create a rudimentary custom RSS aggregator using this powerful library.

He helps you get SimplePie installed (downloaded and unpacked) pulling in both single and multiple feeds. There's no caching or storage included in the tutorial, but it would be recommended if you choose this as an option for everyday use.