Further sources of help

Footnotes (or endnotes) on Web pages
A good reference source for more detail on creating endnotes. Lots of other good stuff on this site by the wonderful Jukka Korpela.
New York Public Library style guide
This guide is elegant and thoroughly useful resource on good practice in XHTML, with the focus on helping people make the transition from old-style mark-up.
Web Design Group HTML 4.0 Reference
Comprehensive reference for the tags and structure of HTML 4.0. The WDG FAQ is very good.
http://www.w3.org/TR/html4/
The definitive low-down on HTML 4.01—the flavour used in XHTML.