There are two ways of doing this - both of which I'm exploring. The first is to go it alone, setting up everything, and the second is to go via an aggregator like Lulu or Smashwords. I'm starting both today and will post how I get on with both methods - including (hopefully) revenue streams with the same cover price.
The first step is to create two ePub books - which is probably the easiest part. I'm using iWork Pages which seems to do the trick, and lets me preview on iPhone and iPad very easily.