"Although it is possible to make most content accessible, it may happen that all or part of a page remains inaccessible. Additional techniques for creating accessible alternatives include:
Here are two techniques for linking to an accessible alternative page:
Provide links at the top of both the main and alternative pages to allow a user to move back and forth between them. For example, at the top of a graphical page include a link to the text-only page, and at the top of a text-only page include a link to the associated graphical page. Ensure that these links are one of the first that users will tab to by placing them at the top of the page, before other links.
"The LINK element may also be used to designate alternative documents. Browsers should load the alternative page automatically based on the user's browser type and preferences." 
If "the user agent is not displaying frames, the user will have access (via a link) to a non-frames version of the same information." 
Copyright © 2001-2003 by Rainer Hillebrand and Thomas Wierlemann