"Anyone actually know? Do I have any alternatives to salvaging what I may be able to pull of the drive and replacing it? Or is this an esoteric, fixable glitch that has nothing to do with hard drive failure?"
I would say that most likely the hard drive is failing. You can check out hardware failures by swapping components. If possible, take the hard drive to another computer and see if it works on the other computer.
The second most likely possibility is that the BIOS has the geometry of the hard drive screwed up. Look in your BIOS for the hard drive configuration settings and see if that can be changed to something that works.
"I had a Knoppix 3.4 cd lying around, so I thought I'd use that to boot the computer up, but when it came up, the boot-up routines didn't see any partition other than hda1 (I wanted to use the lilo.conf from the linux partition on hda). I did an fdisk, and fdisk replied with "Unable to seek on /dev/hda"."
Considered by itself this could be interpreted as a bad partition table. When you throw in the lilo messages, etc I would change the interpretation to: the portion of the hard drive containing the partition table has physical damage.
It is possible that you could salvage the part of the hard drive which is still OK (perhaps most of it) by downloading a low level format utility from your drive manufacturer and doing a low level format on the drive. Doing a low level format can take hours (my 30G Maxtor took 2.5 hours). It will completely erase all information on the hard drive. And after all that work the hard drive may still be unusable.
Obviously you should back up anything that you can before swapping hard drives or doing a low level format.
Be prepared. Create a LifeBoat CD.