For more information on making sites accessible using HTML 4.0, I recommend beginning at the source, the W3C's Accessibility Initiative (WAI). You can read about WAI's activities by visiting www.w3.org/WAI. Detailed information on methodology and code for accessible sites can be found at www.w3.org/WAI-WEBCONTENT.
Other resources abound. WebABLE is dedicated to educating, researching, and developing technologies that make the Web more accessible. Its site is extremely comprehensive, and can be found at www.webable.com.
Finally, the Trace Center at the University of Wisconsin is playing an extremely powerful role in the accessibility movement in general, and specifically for the Web. Check out the Web accessibility information at www.trace.wisc.edu/world/web. --MH