You can use iBooks Author, there are "Chapter breaks" and each chapter can hold a number of "Sections" or " sub chapters" also... you can change/add different styles to each chapter.
There or Portrait and Landscape free templates to choose from.
I can agree with Dan about Redjumper 0 its actually a neat little app for use on iPads - not iMac of any type ( pity really its good!) Check out the app store for "Book Creator" there is a triial version but.. the app is way underpriced. Like iBA it creates an hybrid type ePub.
I use it a lot - and thats my only connections with it!