Intel wrote back and just reinforced that their UPnP stack isnt supported ... thanks for nothing.
so i hacked up their network stack and can get the GET requests for images now. then i look up what image the item ID is mapped to and serve that image. that provides basic UPnP picture browsing to the xbox 360. 'Play Slideshow' even works if you are in a folder that has images. if not, it does a Search instead of a Browse, and i dont have that implemented yet (if ever).
anyway, now i can cook up some more features.