I have used BSDPy with MacBook1,1's. By 'legacy' do you mean PPC? What
size RAMdisk are you specifying in your rc.netboot? If these machines
only have 1gb of ram, you would need to go down to a 256mb RAMdisk.
This happens with most gui apps that run as root. The 'app' in your dock
is just a script that launches another app as another user. They both
happen to have the same icon, so you see two while it is running.