Though there are many resources of varying quality on the 'net, a great place to start reading about earth-centered religions is a book by NPR's Margot Adler called DRAWING DOWN THE MOON. I have several friends who are practicing pagans, and having been raised Catholic, I had my own stuff to 'get over' and learn about. This book was a great help.
I have found this truth when studying ANY religious tradition with an open, searching heart: there is much to learn from, much to admire, and when you get down to the bottom, all that REALLY matters is how/that we love each other every day, and how/that we care for this earth we're on for such a short time.
Here's a little more about Margot Adler, and I think her book's fairly easy to find.