How can I set up the URL for a category archive for a custom post type?

How can I set up the URL for a category archive for a custom post type? References I\'m working on a site www.site.com that has an additional post type: project. In registering project, I\'ve declared \"taxonomies\"=>array(\"category\") so that I can categorize the essays. Works fine. Now, the post type archive is at www.site.com/projects/ as I\'d expected, but I can\'t seem to find a URL for a category archive that fetches only projects. I\'d like it to appear at www.site.com/projects/category1. I\'ve tried every combination of permalink/CPT registration options I could think of, but the best I\'ve gotten was a 404. I am able to get the results I want if I manually enter ?category_name=category1 in the URL but can\'t seem to incorporate this into the permalink structure. Any hints?