You're looking in the wrong place. From the K menu > System > More Programs > File Manager Super User Mode.

Use this to navigate to /etc/fstab

Open fstab in any text editor and remove the # from each line under
# partitions found by Knoppix

one of which will be the hard drive you want. Save the edited file.

Reboot.

then do (as root) mount -t vfat /dev/hd?? /mnt

or mount -t ntfs /dev/hd?? /mnt

depending on whether the file system is vfat or ntfs

the hd?? would be hda for the first hard drive (primary master) hdb for the primary slave and so on. The first partition is represented by hd?1 and so on.

You'll see clues by reading /etc/fstab