Personally, I can't stand root beer, but for those who do, Ananda has two interesting sections on her blog http://www.plantjourneys.blogspot.com/
detailing how her children went out into her back wilderness and dug up a sassafrass root which she then made into root beer - with contemporaneous photos.
Stephen Buhner has a book called "Sacred and Herbal Healing Beers: The Secrets of Ancient Fermentation" which everyone seems to rave about. I've not read it yet as I don't drink a lot of alcohol (despite the vast numbers of vodka bottles lying around my house!) and don't have the time to experiment.