Hi Matthew,
Unfortunatelly, this issue is quite common. News aggregator UI doesn't have the option to delete old items, and this kind of thing usually happens when your server is significantly old to have lots of news feeds.
We have solved the problem building an UI where you can delete the feed entries. Take a look at your code and see if it can be usefull to you: http://svn.softwarepublico.gov.br/svn/openacs/branches/spb-2.0/packages/news-aggregator/
