you should just change permissions to something like 640 (rw-r----) or 740 (rwer---) on the usb device.this would allow things like usb keys and mice and the drive bout would not allow them to execute or to write to those drives.

as for the sudo command:

http://www.google.com/search?q=cache...ient=firefox-a
<sorry for the long url google cache>

sounds to me like your sudo file is messed up. i would follow this site to find out whats wrong

this one is also a good one if the above doesnt want to work.
http://www.linuxhelp.ca/guides/sudo/

i would also ask on the fourms at
http://www.linuxquestions.org
if these things dont work