Perhaps somone has already done this., but I was able to hexedit the Knoppix.iso. I boot with Knoppix 3.6 and in particular with PC does not like DMA nor does it like the hires console since the monitor gets all blurry.
Code:
knoppix 2 nodma vga=normal
Code:
# mount -t ext3 /dev/hda6 /mnt/hda6
# cd /mnt/hda6/mnt/test
# hexedit Knoppix.iso
<Tab> to switch to ascii mode
<ctrl-s> to search
DEFAULT linux24
<Enter>
navigate to vga=791 and type nodma plus 2 spaces -> 'nodma '
<ctrl-x> to save and exit
Burn modified Knoppix.iso & boot off it. IT WORKED! The PC will now boot by default with nodma and will boot in a normal vga console & not a hight res console.

I hope this helps.
James