if the harddrive is part of a computer just connect it (the computer) with your mpc. you can now just drag and drop your samples from your hdd to the compact flash card or hard drive. if your computer has a card-reader build in you can put the cf directly to your computer and drag the samples there.
if your hdd isn't connected to a computer there is no way to directly plug it to your mpc. the drive won't show up.