Does this discussion help? It's kind of a stream of consciousness thing, but you can see the thought processes of the OP, who came up with a solution, and some alternative (better) solutions. It may not be exactly what you want, but it should get the lightbulb on in your head. The example of creating the functions.php file and using author.php for the call to the code in the functions file is the best route, because as stated in this thread, you don't have to worry about overwriting any core files during an upgrade. The technique discussed here lists all authors in a list, whether they've posted or not. Which wp_list_authors won't do; it just lists authors who have posts.