Hi,
I created an ePub authoring tool (freeware, Windows) called ePuper that might be useful for you.
Basically ePuper was written to bring online newspapers to an ebook. ePuper has an interface for which you can create plugins that convert your favourite web page to an epub file.
If you create an ePub by yourself, all management of files, XML and index entries is done by ePuper. You can concentrate on putting HTML content to the chapters.
The new version 0.2 speaks English and has a few new features. Check out
http://www.epuper.de/ for download and more information.
Important: Give me some feedback of what you like and what probably not...
Have fun,
A.K.