Are you sure you want HID. That is for keyboards and mice. http://en.wikipedia.org/wiki/USB_human_interface_device_class
Doing mass storage may work better. The Overo board would appear to be a USB thumb drive. You would be able to access and write files from almost any USB host.

Look at the Linux documentation for Gadget drivers and http://www.linux-usb.org/ for a ton of info.

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