Docbook was created more than 10 years ago, but since 1999, Docbook has been under the guidance of the DocBook Technical Committee at OASIS. The OASIS website distributes the official DocBook DTDs, and has pages on Docbook history, samples, tools, and runs a few docbook mailing lists.
Since the Linux Documentation Project uses docbook, they have written some good tutorial material. In particular the LDP Author Guide, by Jorge Godoy is very good.
O'Reilly & Associates publishes a book called DocBook: The Definitive Guide by Norman Walsh and Leonard Muellner. You can buy it or read it online. Norman Walsh knows what he's talking about, since he is the chair of the DocBook Technical Committee. This is good for reference, since it has a complete list of tags and their grammar.
An article on lwn.net called Exploring SGML Docbook focuses mostly on installation of tools from scratch: openjade, Norman Walsh's DSSSL stylesheets, and jade2tex. If you can get the tools from RPMs or whatever package your OS uses, use that instead.