This is quite a nice idea. However there is a problem:

Sometimes knoppix does boot, but you get many read errors with dma on.

Why don't you just set dma off and are done?

You can set it up on the old machines later one from your NX-startup scripts.

Like that:

Code:
        # Enable DMA for all IDE drives now if requested (if not already done by linuxrc).
        # This is already done by linuxrc now.
        # However, for a harddisk-installed version, we are doing it again here.
        # Please use hda=dma or similar in the lilo.conf append= line.
        for d in $(cd /proc/ide 2>/dev/null && echo hd[a-z])
        do
                if test -d /proc/ide/$d; then
                if egrep -q 'using_dma[ \t]+0' /proc/ide/$d/settings 2>/dev/null
                then
                        MODEL="$(cat /proc/ide/$d/model 2>/dev/null)"
                        test -z "$MODEL" && MODEL="[GENERIC IDE DEVICE]"
                        echo "${BLUE}Enabling DMA acceleration for: ${MAGENTA}$d        ${YELLOW}[${MODEL}]${NORMAL}"
                        echo "using_dma:1" >/proc/ide/$d/settings
                fi
                fi
        done
cu

Fabian