This is really great, Zelda. It hasn't been that long since I last re-read the book, but this illustrated edition deserves to be next on my reading list, and the markup and css itself is almost as beautiful as the book.
A couple of problems though.
You used the wrong alt text for the initial letter in chapter 1 (the initial letters in the other chapters seemed fine though):
<div class="lettrine"><img src="images/t.gif" alt="W" /></div>
You should limit alt text for cases when it's actually required. The alt attribute is meant to be used when a visually impaired reader would not be able to follow the text without knowing what an image is of. A blind person really isn't going to care that some illustration he can't see is of a "man with cane". If an image actually contains text that a blind person can't read, such as header1.gif or the initial chapter letter images, then you should use alt text, but in many cases, alt="" is really the best thing to do.
Take the first illustration in chapter 1, for example. This is what the book would sound like to a blind person:
The diagnosis seems in every case to correspond exactly with all the sensations that I have ever felt.
Reading up on ailments. I remember going to the British Museum one day [...]
See "Context is Everything" at http://webaim.org/techniques/alttext/
, specifically example 2.