"About 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"

See linked page for system requirements. (Also available for windows.)
(As of this post time (11AM ET), the apple security updates page (HT1222) hasn't been updated with a link on any iTunes 10.5.3 fixes. Above may just be boilerplate text.)
  

• Apple Education Event Keynote video
• Apple Unveils iTunes U App for iPad, iPhone & iPod touch (press release)
• Apple Reinvents Textbooks with iBooks 2 for iPad (press release)
• Apple in Education (web page)
• iBooks Author (product page)
• The all-new iTunes U (product page)
• iBooks Textbook for iPad (product page)
• Live from Apple's education event at the Guggenheim (forbes)

• iBooks Author: Publishing and distribution FAQ
• iBooks Author: Best practices for using 3D models
• iBooks Author: Add video to your iBooks
• iBooks Author: How to make your iBooks accessible
• iBooks Author: Use iPad-safe fonts when authoring books
• iBooks Author: About the Keynote widget
• iTunes U: Frequently asked questions
• iTunes U: How to access iTunes U Course Manager
• iTunes accounts for students
• MacBook Air (Late 2010) and later, MacBook Pro (Early 2011), iMac (Mid 2011 and later), Mac mini (Mid 2011): Recovering a lost firmware password
• Intel-based Macs: Resetting the System Management Controller (SMC)
• iTunes: Troubleshooting security software issues
• iOS: Third-party Bluetooth headsets, headphones, and keyboards
• iOS: Device not recognized in iTunes for Windows
• About the Apple Store app
• OS X Lion, Mac OS X v10.6: Printer and scanner software
  (updated for Brother driver update Tues.)
• iTunes for Windows: May quit unexpectedly when playing protected content from iTunes Store
• iPhone and iPod touch: How to configure Exchange Mail settings to increase or reduce the amount of emails displayed on the device
• Mac OS: Web Browser Quits Unexpectedly or Stops Responding (archived/no longer updated)
• Bonjour for Windows: Password required when using security software (archived/no longer updated)