Now I have neither a rhe or Knoppix install so I've no idea what kernel they use. init=5 is not even necessary. You can remove it.

If you installed Knoppix to /dev/hda2 then root=/dev/hda2
GRUB sees things differently. (hd0,1) = /dev/hda2

I would probably try this in GRUB.

Code:
title Knoppix
kernel (hd0,1)/boot/vmlinuz-2.4.27 root=/dev/hda2 nolapic acpi=on nodma ro vga=791
initrd (hd0,1)/boot/initrd.img-2.4.27
savedefault
vga=791 is not required but it gets you the framebuffer device.