Comment 19 for bug 26426

This issue affects Lucid on G3 iMacs too.

Installing Kenneth Finnegan's yaboot binary from comment #18 to the TFTP server solves the issue. Both vmlinuz and initrd load, and the kernel starts. Sizes are:

/var/lib/tftpboot$ ls -l iso-image/ubuntu-10.04-desktop-powerpc/casper/powerpc/
total 18360
-r--r--r-- 2 root root 9241444 2010-04-28 14:37 initrd
-r--r--r-- 2 root root 9558100 2010-04-16 12:44 vmlinux

/var/lib/tftpboot$ ls -l yaboot*
-r--r--r-- 1 root root 163886 2010-05-18 06:18 yaboot
-rw-r--r-- 1 root root 295 2010-05-18 05:26 yaboot.conf

/var/lib/tftpboot$ cat yaboot.conf
device=enet:
partition=0
timeout=60
init-message="Ubuntu GNU/Linux NetBoot"
default=ubuntu-10.04-desktop-powerpc

image=/iso-image/ubuntu-10.04-desktop-powerpc/casper/powerpc/vmlinux
    label=ubuntu-10.04-desktop-powerpc
    initrd=/iso-image/ubuntu-10.04-desktop-powerpc/casper/powerpc/initrd

This currently boots to busybox since I've not yet added the NFS root to the kernel's command-line, but hopefully it will help others.