jaymis

I think Query Posts will be the magic sauce for this one, but I’m not really sure how I’d go about it.

This seems to be a similar problem, and proposed solution:
http://stackoverflow.com/questions/1014269/wordpress-producing-a-list-of-posts-filtered-by-tag-and-then-category

For a less hacky method, something like this may help: http://yoast.com/wordpress/simple-taxonomies/

It would require some re-taxonomification of your existing content though.

Jaymis