Thru trial-and-error I (partially) solved my problem with my unmountable LS-120 drive. I had been trying to mount it as /dev/hdd, which is how the bootup messages recognize it.
I poked around /dev and tried every /dev I knew (or thought or read somewhere) to work with a disk or disk-like device, i.e., /dev/hd? /dev/scd? /dev/sr? /dev/sg? /dev/sd? (the list goes on). I finally succeeded in mounting it as dev/sda, but as a read-only system. Question: Is there a more scientific way to go about finding the proper /dev for my devices? Is there a HOWTO, or rather a WHATIS (as in, What is this little red button supposed to do?) doc that can tell me which device each of the /dev files in my system works with? All I need is a simple list like: /dev/hd? --> IDE hard disk /dev/sg? --> cdwriter