Change the sorting order used for Book nodes
You should checkout the Book helper module.


  The Book helper module enables additional features from Drupal's menu system to improve the ordering of a book's pages. This module also allows administrators to further customize a book's navigation block.
  
  Features
  
  
  Enhances the book outline manager
  Adds 'enable' checkbox (aka hidden) to the manage book outline page
  Adds an 'Order' tab (node/%/order) to a book's main page
  Adds 'administer own book outlines' permission for ordering books from a book's main page
  Removes the 'Outline' tab from all nodes
  Removes the book fieldset from node edit pages if the content type does not allowed book outlines
  Removes 'add child page' and 'printer-friendly version'
  Removes book navigation
  Customizes visibility of a book's navigation elements
  Automatically 'Create new book' for selected content types
  Includes 'Book (inline) navigation' block that can be easily positioned after a node's content
  Disables new revisions from being created when a book's node title is updated
  Displays a warning when deleting a book page (node/%/delete) that has child pages