Jensen FV, 'An Introduction to Bayesian Networks' , UCL Press, 1996. ISBN 1-85728-332-5 HB.
A reasonable introduction that comes with a demo version of Hugin.
Pearl J, 'Probabilistic reasoning in intelligent systems' , Morgan Kaufmann,
Palo Alto, CA, 1988.
This book contains a thorough, but very hard going, account of BBNs and their propagation