This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
I don't think there are any freely available books on this subject. But actually, it's a small subject, and there may not be any books that cover it exclusively. The Sun Java Tutorial has a chapter on Web Start that should teach you most (if not all) you need to know about it.