Both include an option labelled My
Computer that can be used to turn off access to specified drive
letters. These options are global-- affecting all users of the
computer, as far as I've seen and remove access to the specified drive
letters in My Computer, Windows Explorer, standard File Open and save
dialogue boxes, etc.... but users in the know can still access hidden
drives by using the Start Menu's Run
command and simply typing (for example) 'C:\' (note that you need to
include the backslash).