Section 508 requires that Federal agencies' electronic and
information technology is accessible to people with disabilities,
including employees and members of the public.

The Access Board is an independent Federal agency devoted to
accessibility for people with disabilities. Comprehensive list of
resources regarding the access board and the law.
http://www.access-board.gov/508.htm

Summary of the law
http://www.access-board.gov/sec508/summary.htm

Review of Web Accessibility issues 4 part article (Part 4 with links to
previous parts)
http://www.webreview.com/2001/03_23/webauthors/index04.shtml