Well O’reilly is an excellent source for technical books. After a brief search I turned up two.
http://www.oreilly.com/catalog/dreammx2004tmm/ http://www.oreilly.com/catalog/bddwsdream/ Aside from books, how I learnt dreamweaver was just messing around with it for a couple of hours. Also Dreamweaver has excellent context sensitive help. You see all the question marks (?) around the place? Click one of them, and you should go to a help entry specific to the thing that it was near to.