I've been researching this and haven't found much in terms of standard solutions for creating a 508-compliant, accessible org chart. We have images that represent organizational structure. It seems like the options would be to create an external file to link to that attempts to represent the relationships in the chart (although I'm not sure if there's a commonly accepted way to do this via text for a hierarchical tree), or maybe create an imagemap that doesn't actually link to anything externally but just exists for the labels. That seems much more of a hack. I also just thought of another potential representation - another html file (linked) that is basically just your standard list, which can represent a unlimited hierarchical complexity. Some labeled items are outside the general hierarchy (so groupings of various types within th hierarchy, etc.). Just wondering if anyone else had run into this, or just seen examples of how others have approached it?
Section 508 says, regarding web-based intranet and internet information and applications, which is probably what matters here: “(a) A text equivalent for every non-text element shall be provided (e.g., via "alt", "longdesc", or in element content).” Any solution that fulfills the requirement is 508 compliant. Note that this is a legal and formal matter; it does not imply that the content is really accessible.
So you can, for example, write a textual description of the organization (equivalent in content to the image) into the alt attribute. There is no defined upper limit on its length. Alternatively, you can use the longdesc attribute to link to a page containing an equivalent description, which may use all the expressive power of HTML, e.g. nested lists, or a table (which has accessibility requirements of course). Software support to longdesc is limited, if not anecdotal, but Section 508 explicitly mentions this possibility. Most sensibly, you can write a textual description, using HTML markup as needed, either in the page content (in which case you can use alt="") or on a separate page that you link to.
For a more specific answer, I think you need to ask a more specific question – like one with a real image representing an org chart.