First, you need to find out in which partition music is stored. Usually, it's like this:
C drive-> /dev/hda1
D drive-> /dev/hda5
E drive-> /dev/hda6
F drive-> /dev/hda7
Note that this is for Primary Master.
If the hard drive is Primary slave, replace hda by hdb
For secondary master, it is hdc and for secondary slave, it is hdd
Now, assuming that your music is stored in E drive,
1: login ass root
2: Create a mount point. This is done by typing "mkdir /mnt/edrive" (without quotes)
3: mount the device on the mount point. This is done by "mount /dev/hda6 /mnt/edrive"
Now, all your music is found at /mnt/edrive.
To mount the partition every time automatically, you need to add the following line at the end of the file /etc/fstab
/dev/hda6 /mnt/edrive vfat defaults 0 0
You can change the file system type if it is not vfat. You can try auto.