Following their education event held in New York where iBooks 2 and textbooks were announced, Apple has gone ahead and released iTunes 10.5.3 to the masses. As noted in the change log, this release covers the ability to sync interactive iBook textbooks to your iPad:
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. For information on the security content of this update, please visit: support.apple.com/kb/HT1222
The update is currently showing on the Apple website and should start rolling out through software updates shortly.