This is normally the point where I say "Hold it, Ill be over in an hour", but thats not an option in this case. (I do have a free week coming up if you fancy paying for it
)
Some thoughts. There is a master on that channel right? Some BIOS will detect a slave without a master, but ive never seen one work correctly.
Try putting the 80Gb in where your 20Gb is - same settings, same cable. If that fails you know youve got a dead drive.
In any case, you shoudnt be having an HDD as slave, you want both HDDs to be masters on different channels, with the CD-ROMS as slaves.
And in order to boot from CD, you need to change the boot sequence in BIOS.