The home of DocBook: The Definitive Guide http://www.docbook.org/
Have a look at the wiki as well: http://wiki.docbook.org/topic
See also http://freshmeat.net/projects/docbook2x/ for a tool to convert DocBook formatted files into Texinfo or man page formatted files.
The docbook sf-project includes xslt and dsssl stylesheets. Normally that would be towards pdf, html, xml, rtf, but I would think tex as well, texinfo I'm not sure about. VL 16/6-03.
Online DocBook Validator and XML -> HTML/PDF Transformer: http://validate.sf.net
I wonder if http://freshmeat.net/projects/remark/ might help convert some docs into this format...