Apple has today released iTunes version 10.5.3 with updates for iBooks textbooks and iBooks Author.
What’s new in iTunes 10.5.3
iTunes 10.5.3 allows you to sync interactive iBooks textbooks to your iPad. These Multi-Touch textbooks are available for purchase from the iTunes Store on your Mac or from the iBookstore included with iBooks 2 on your iPad.
iBooks textbooks are created with iBooks Author — now available as a free download on the Mac App Store