For the blinds it’s very difficult to handle the manager of MODx. First problem is the use of frames because of difficult navigation of frames. AJAX is a nono at this time because of impossibility detecting changed states of an element. Form elements need labels for each field, Javascript won’t work, especially mouse dependent events (mouseover, onmouseout, ...).
A first impression to you: Use Firefox with the Web Developer Toolbar add-on. Disable all styles in toolbar’s CSS menu. Is the manager usable for you in this case? Note that you can’t see the content but hear it. The screenreader will read loud the content of each frame from top to bottom of the source code (without reading the tags). Screenreaders will read "heading" (and their level), "(un)ordered list", "list item", "link", "email" at the corresponding content to mark the special element. Following a link is possible by pushing the enter key. There are short keys for reading an overview of (HTML) headings or link lists to quick "scanning" the content of a page.
You can install yourself a test version of the JAWS screenreader. It works for 40 minutes then you need to reboot the computer for a further test period. The JAWS you’ll find at:
http://www.freedomscientific.com/fs_downloads/jaws.asp
