Intro to Book Packaging
Not very long ago, I tried explaining what a book packager does; and, trying to keep it to just a few sentences, I didn't do a very good job of it. So I'm letting others explain it better. Wikipedia has a pretty good explanation, and there's an article at Absolute Write as well.
I should mention that, in my own experience, packagers are best served by not handling the printing of a project. Most publishing houses have production staff for working out deals with print houses (most nonfiction is printed in Asia), so the packager would just produce the book and provide it to the publisher in printer-ready files.
It will be interesting to note, as everything is digitized, how quick nonfiction books become e-books. You might find out by attending some of the American Book Producers Association's lunch events, where guest editors discuss opportunities for packagers. You don't have to be a member, and these are jewels of opportunities since "outsiders" rarely get the chance to eavesdrop at will.