DocBook is a widely used DTD in SGML and XML that is tailored toward technical manuals. It's basically a way that authors can write a document once and then using SGML and XML tools to convert to many common formats (HTML, DOC, RTF, PDF, PostScript etc.). It is used on a huge number of open source projects as the main documentation system.
I'm working on a HOWTO/book. These are my notes from a three month bout with these tools and concepts. I had a difficult and frustrating time setting up these tools. Plus, I couldn't find a working equivalent. So, I truly hope this information will be helpful, but it is provided without warranty or gaurantee. If you break anything you get to keep both pieces.
This guide tends toward the DocBook spirit. I assume authors don't need to get mired in a gajillion layers of DocBook complexity just to generate an articulate piece of work. More simply: Get tools, write content and distribute.
Please, note that I do not cover the installation or usage of some of the 'fluffy' tools like docbook2X or sgml-tools. Nor do I make mention of backends other than html and text. I leave it as an exercise for the reader to generate different types of output (tex, pdf, etc.). This document is intended to be the straightest path to writing and evaluating your documents.