hard drive password

Windows does not support password protecting HD's how ever there is software that you can use to encrypt the drive.
http://www.truecrypt.org/ and its free.

If you are trying just to restrict access to one drive on a shared PC, You could remove the accounts access to the drive by simply right clicking the drive go to the secutiy tab and remove the accounts that are not meant to have access, this can also be done for folders and files. But if they have a adminstrator's account they can remove it just as easiliy if they know what they are doing...

hope this helps.