Whilst looking for information on how to make our MOSS 2007 Internet sites compliant with accessibility guidelines I found the following great post from Andrew Woodward -

http://www.21apps.com/2007/03/sharepoint-accessibility-is-moss-2007_4974.html

If you use ASP.Net controls like the menu controls in your MOSS Internet sites these will be rendered using tables. To make the controls nice and accessible you can try using the css adapters found here -

http://www.sharepointblogs.com/mossman/archive/2007/03/08/css-friendly-control-adapters-in-sharepoint-2007-a-walk-through.aspx

The only downside of installing these on your sites is that they seem to make a bit of a mess of the site settings and manage content pages.