Multimedia content on the Web, by its definition - including or involving the use of several media - would seem to be inherently accessible or easily made accessible.
However, if the information is audio, such as a RealAudio feed from a news conference or the proceedings in a courtroom, a person who is deaf or hard of hearing cannot access that content unless provision is made for a visual presentation of audio content. Similarly, if the content is pure video, a blind person or a person with severe vision loss will miss the message without the important information in the video being described.
Remember from an earlier lesson that to be compliant with Section 508, you must include text equivalents for all non-text content. Besides including alternative text for images and image map areas, you need to provide textual equivalents for audio and more generally for multimedia content.