yea getdataback might work. it will try to recover the parts of the drive it can read.
your parents didn't heed the advice to backup eh?
get them a mac with time machine

i swear that kinda consumer friendly backup shoulda been standard long ago.. on a second internal drive.
but consumers are too stupid and cheap for their own good for that to have worked.
i'm not sure about knoppix. the point of that is to boot the cd/dvd os so you can read off the drive. but if the drive is slightly scrambled knoppix will probably freak out and won't be able to see the contents or not be able to recover much. actual recovery software tries much harder to recover data most o/s's can't see. i remember one of my drives going bonkers, windows would just tell me to format the "blank" disk, the recovery software could after a long period of scanning the drive recovery a decent bit of stuff. maybe knoppix has recovery stuff now, its been a while since i downloaded that distro

course just because a recovery software can force read some stuff doesn't mean it will be perfect. some of my pictures were slightly corrupt and stuff.