A few notes i made whilst investigating.
ISBN
You will need ISBNs for all titles you intend to distribute
UK http://www.isbn.nielsenbook.co.uk/uploads/3971_ISBN_Application_Form_2012_WEB.pdf
USA http://www.isbn.org/standards/home/index.asp
How to publish a book to the Kindle:
http://blogkindle.com/2010/11/how-to-publish-a-kindle-ebook/
How to publish to iBooks
http://www.tuaw.com/2010/01/31/all-about-epub-the-ebook-standard-for-apples-ibookstore/
Useful tools:
For Mac users, the choice of tools is small, but good. First, there’s the free Calibre ebook management tool.
For formatting, you’ll need a full-powered EPUB editor. Sigil is a free open-source editor.
Next, there’s the inexpensive (US$49.99 for a single license) iStudio Publisher.
If you happen to be an Adobe InDesign CS4 (US$699) user, you’re in luck. publishing supports EPUB and will also work on both iBooks and the Kindle