How can I create an author widget

Hey, All -

I'm brand new to WordPress, and was told to use the Atahualpa theme to make my first foray a bit easier. So far it's working, but there's one thing I can't figure out how to do:

I figured out how to make a link in the byline of a post that brings up all of a particular author's posts, but I want to create a widget that I can place in the sidebar with the names of all of the authors on the site, so someone can click on a particular author at any time and bring up all of their posts.

What's the easiest way to do that?