"This might be better on SuperUser or ServerFault. Directly I do not know of any way to do this, it might be better to know what O/S you are trying to accomplish this under. You could use TrueCrypt or something similar to encrypt the disk at the volume level. However with TrueCrypt it would not prompt you for the password necessarily, it would just show the drive as full of white noise (i.e. unformatted), you would have to know to load the driver for mounting the volume and provide the appropriate password.
It should also be noted that TrueCrypt (and BitLocker as well) have been shown to have a flaw which does allow someone to intercept the loading of the secure driver and pre-empt the password verification routine giving them access to the password. This attack is non-trivial to accomplish and does require physical access to the device. You can read about the Evil Maid attack here."
