Donb:
I too have the same issue (unable to print using Knoppix v5.0.1 LiveCD).
Tried everything in your post (& tried all the available drivers listed for my printer) and still cannot print to an HP720c connected to a parallel port on my PC.
During the setup, Knoppix recognizes that the HP720c is there on the parallel port.

When I print, I see a message flash (flash message is too fast to read, but it appears to be a message that it has sent the job to the printer). When I check, it shows that the print job completed, but the printer is not receiving it.

Printing works fine in Windows XP, so I know the hardware is working.

If you, or others in this forum, have any ideas on how I can make it print, I would be most grateful.

Thanks,
wazzy