David Brody's book "Fiddler's Fakebook" has some intro about the various styles. Still, the written word conveys a very imperfect image of the styles. Fatten up your CD collection and spend time listening. Subscribe to "Fiddler" Magazine, which represents all styles. If you subscribe for three years (and you ought to), you get a free 1999 tune-a-month calendar and CD with the tunes on the calendar played in practically every style you can name.