I just had the problem, that a machine did manage to mount the FAI nfsroot. It properly boot with PXE from network card and get its kernel and initramfs via TFTP. Then the kernel boot, the initrd start but the IP-Config call hangs and gets no reply from the DHCP server. This was caused by a broken ipconfig utility that only occurs when you are using a DHCP relay/gateway between your machine and the DHCP server. ipconfig is a small tool included inside the initrd that is created by mkinitramfs. More info about the bug can be found here: http://bugs.debian.org/432977
The fix was to add a new klibc-utils and libklibc package (>=1.5.9) into the nfsroot and rebuild the initrd with dpkg-reconfigure linux-image....... Use can use those packages also in an etch nfsroot. The machine had two network cards, so in the beginning I thought it's the problem of switching assignment of the two cards (eth0 <-> eth1), but that was not the case. -- regards Thomas
