how can i reorder another photo book i already have

You have to go thru iPhoto and order as if it were a new book. For future books create a new library just for that book, transfer the photos needed to it with iPhoto Library Manager. When finished the library can be saved to a CD or DVD disk for storage until another copy is desired.

Here's a suggestion for the current book in your library: iP12 - Archiving an iPhoto 9 (11) Book for Editing and/or Ordering at a Later Date

OT