Indexing Custom Taxonomy/Categories/Tags

Does anyone know how the following might be achieved - plugins etc.

I am trying to display a page of aggregated posts that are full of custom taxonomy. The pages are a similar concept to Justin Tadlock's Movie Database -
justintadlock.com/archives/2009/06/04/using-custom-taxonomies-to-create-a-movie-database

However I have a collection of sites that I want to be able to draw posts from onto one page and then build a search function for.

From what I can tell from the forum the Post Indexer is not going to be able to able to help with this as it only indexes the posts table. Is there anything else out there in the way of plugins that might be able to help???? If not would you consider building it? It would be great for building networks selling cars, real estate etc