The W3C Web Accessibility Initiative at http://www.w3.org/WAI/ provides a great deal of practical information about designing applications and interfaces for the broadest range of users. Macromedia supports user accessibility in its product interfaces and is striving to fully implement the WAI recommendations.
Simple steps, such as providing a text alternative for images, graphics, and animations, and using clear descriptive text for page elements and navigation, can make a world of difference to a visually impaired user's experience of your site. Validation tools are available on the site to check compliance with established standards.
Standards may change more quickly than the product, but you can script the Visual Tools Object Model (VTOM) to extend or manipulate its functionality. For details, please see "Customizing the Development Environment" and "Scripting the Visual Tools Object Model". You can also check HomeSite Help site for free downloads that extend the accessibility capabilities of HomeSite.