Delete old posts in a single category

I am posting from an rss feed and need to delete posts in that category that are more than a month old. I have found a few plugins that come close, but are as much work as just doing it through WP 2.5.1:

Batch categories: can’t figure out how to set categories for more than 15 posts at a time (am I missing something? can’t find a way to contact author or find help). Presumably, you set all your unwanted posts to a certain category, then delete them all.

Auto delete: seems very old (2005)–WP 2.5 compatible?

Simple tags: still not a batch option.

Thanks!