If you need to tweak the styles of your ebook created with the iPad in mind then you can (with a bit of magic) set up Dreamweaver as a useful wysiwy(almost)g tool.
Dreamweaver, is, of course a web development and design tool. It will normally handle (x)HTML without any change. It will also allow you to edit other code and even XML. It will not edit the contents of a ZIP file (this is what a normal ePub package is) unless it is unpacked.
The Adobe AIR application used to be a free download. It was useful because you could edit an ePUB file without needing to unpack it and re-zip it. I used it in my class to show how to edit XHTML and CSS.