Bayesian Network for dummies

Bayesian Networks are also known as Graphical Models. An excellent (free sample) chapter (author's or publisher's version) on the subject is in Bishop's book, Pattern Recognition and Machine Learning. See also this post, the bnt toolbox, and example studies such as this one on modeling lung cancer diagnosis. My favorite book on the subject is Borgelt's 2009 2nd edition of Graphical Models.