It's available at Packt now! http://www.packtpub.com/jboss-esb-beginners-guide/book
And at Amazon: http://www.amazon.com/JBoss-ESB-Beginners-Guide-DiMaggio/dp/1849516588/
A review of the book is here: http://rickwagner.blogspot.com/2011/10/book-review-for-jboss-esb-beginners.html