"Instead of just holding N when booting hold 'option', all available ones or "active" nbi's on your netboot server should appear there. "
holding option doesn't show any netboot. you have to also press n after the boot menu comes up. and no, only the server ip address comes up. i heard rumors that only some models the nbis actually show up. i can't believe apple misses the boat on this one. windows server gives you a nice menu with all the boot images. i can't run multiple servers like an apple store can for netboot