Hi romi,
already tried that
disk utility has indeed an option to eject or deactivate the device. But no luck , the cybook sends the signal to reconnect I watched the konsole messages and it confirms my theorie. I see how the system disconnects the devices and soon afterwards it's reconnected.
What I do now is starting a virtualbox image (similiar to vmware but free) with a Windows XP and use the safely remove hardware button. Then it works.