That is the free space on your hard drive. (read: unpartitioned) you must partion it, create a filesystem on it, and mount it before you can use it.
EX: (as root)
# parted /dev/hda
> mkpartfs primary ext2 1021 37040
# tune2fs -j /dev/hda3
# vi /etc/fstab
(add this line to the bottom of the file)
/dev/hda3 /mnt/medic ext3 defaults 1 2
(then save the file)
# mkdir /mnt/medic
# mount /mnt/medic
# df -h
you should then see your new partition.