Password protecting a drive

I have a client that wants a harddrive installed, that only he has access to. Installing the harddrive and assigning it is no problem. What I need to know is how do I either hide it from view from users of that computer(and network) other than him? This is NOT a network question. I know how to un-share the drive or the whole computer. I just need to hide the drive or password protect access to it.