Well, I had a few minutes, but no more, to look at it again. First, I never use image maps like this, and I’m not sure I’ve seen one used for a tab navigation like this before. As an aside, the design would be more accessible to older browsers and screen readers if you implemented the navigation as an unordered list, and used an image replacement technique to add the tab graphics you’ve designed.
Anyway, if I save the file to disk, using Safari, I can view the site without the style sheets loading. When I do this the Nav WORKS, appears and the map areas are clickable (though everything else looks funky and unstyled of course. I have to assume there’s something in your styles as they are applied to the #navigation id that is being read by safari in a way that causes the image not to display—since it is otherwise holding its place in the layout (there’s just an empty space, with the background gradient showing through. Maybe use a CSS validator to look for syntax errors in styles that affect the #navigation id.
Sorry that’s not more definitive, post a message if you figure out the fix!