Here is a sampling of links dealing with astrophotography. I'm sure there are many more I have not listed, however these should provide a good start to those seeking additonal information!
"Astrophotography for the Amateur", a book by Michael Covington. This is a great book, I have learned a lot from the material within it. I have the revised edition (1991), a new edition recently came out (it was reviewed recently by Sky and Telescope). Here is a link from which you can sample part of the book and order it:
http://www.covingtoninnovations.com/astro/
Jerry Lodriguss' "Catching the Light" page: A suberb and quite comprehensive site dealing with everything from beginner to highly advanced astrophotography. Highly recommended site.