I've still got a few Netra X1's running.
From my notes:
First thing after booting the tftpimage jump to a shell and:
modprobe -r dmfe
modprobe -r tulip
Then you can continue the install.
After it reboots to the new system:
echo 'blacklist dmfe' > /etc/modprobe.d/dmfe-blacklist
If all else fails you could track down and delete dmfe.ko but you'd have
to remember to do that after every kernel upgrade. The above method worked
fine on my production boxes.