I picked this up from
Current Cites - a useful e-mail newsletter, and
also a Web site. Eric Lease Morgan has produced an introduction to XML,
Getting started with XML, specifically for librarians and library staff, although I think it will be equally useful to anyone who things of themselves as an information manager or even a knowledge manager. The guide is available as a .pdf file and as an html file, as well as .zip and .tar.gz files, which include sample files. An introduction to XHTML is also provided, as a 'dialect' of XML - this might prove useful, as I hope to move from html to xhtml with volume 9 of the journal.
The guide is part of Morgan's own Web site, Infomotions, which also includes 'Musings on information and librarianship', his monthly column for Computers in libraries.