InDesignSecrets

Apple says it's supporting the ePub format, but it's not saying much else. At the moment, if you do a search of Apple's site for ePub, you get a link to information about a Mac program called iStudio Publisher (more on that later.)

But there are other applications that support ePub, most notably, Adobe InDesign. This blog on InDesign will probably be a useful resource: InDesignSecrets.com

Also, check this guide from Adobe on creating ePub documents with InDesign.