To restore your files from a hard drive, you must first log in to your account online to select files, then choose Ship on Media as the delivery method. You cannot choose hard drive specifically; files arrive on a hard drive only if the total size of all files is sufficiently large.
To unlock the shipping encryption for the files on the hard drive, you will need the key which is emailed to you separately. You may need to look in your email's spam or junk folder. If you lose this key, please request assistance here: http://support.mozy.com/support/restorehelpform.
You use a program called TrueCrypt, which is provided on the hard drive. TrueCrypt restore volumes are named data.tc. These restore volumes cannot be larger than 250 GB. If the total size of all your files to restore is larger than 250 GB, there is more than one TrueCrypt volume on the hard drive, each inside a separate folder.