I'm not sure how much of this mandrake does automatically, but all in all what you would do is this:
From a console type su to become root, then type:
mkdir /mnt/<what you want to call it>
mount /dev/hd## /mnt/<what you called it>
where the ## is going to be the drive, if it is a seperate hard drive with one partition then it will likely be hdb1. if it is a different partition on the same drive, then it will be hda# whatever number the partition is.
after that you can access the files. if you cannot access as a regular user then you will need to do (as root again)
chmod 777 /mnt/<what you called it>
This will open the permissions wide up.
After it is working, then you can go to google.com/linux and search for fstab to see how to make it mount automatically at boot, or more ideally search for howto automount (better solution, but more steps to set up)