I had just gotten through "Hello World" on a PalmOS simulator when I saw this press release from ACCESS. Apparently, there is already an ePub reader using NetFront:
http://www.access-company.com/news/p...21_1_epub.html
I went browsing in ACCESS's Japan site which has more interesting info (you'll have to make your browser translate).
http://jp.access-company.com/product...ublishing.html
I've not seen any signs of the actual NetFront ePub reader software, but it sounds like it does exist.