Googling around you sometimes run into useful stuff- here's a web edition of a book on accessibility: http://joeclark.org/book/sashay/serialization/home.html Very thorough (accessible porn...? ) but much more comprehensible than that WCAG stuff. (or was it WACG ). Have a look at the chapter on images for example.
Just read the first section (The Access Manifesto) and it sounds like it's going to be really good. Thanks John.