I'm having the same boot problem, and also not finding any answers.
I have just installed Ubuntu warty via the Knoppix Live CD today; install went fine, all the packages arrived in their places without a problem. Then I configured my apt sources.list and told it to go fetch me some kernel images, and I've ended up with both vmlinuz-18.104.22.168-3-386 and vmlinuz-22.214.171.124-3-686 and their corresponding initrd.img files in my /boot partition. I've got
root@Knoppix:/ # df -h
Filesystem Size Used Avail Use% Mounted on
/dev/hda3 9.7G 457M 9.3G 5% /
devpts 9.7G 457M 9.3G 5% /dev/pts
tmpfs 9.7G 457M 9.3G 5% /dev/shm
/dev/hda1 29G 23G 5.4G 82% /mnt/windows
/dev/hda2 99M 24M 71M 25% /boot
/dev/hda6 5.6G 33M 5.6G 1% /home
root@Knoppix:/ # cat /etc/fstab | grep -v ^#
/proc /proc proc defaults 0 0
/sys /sys sysfs noauto 0 0
/dev/fd0 /mnt/floppy auto user,noauto,exec,sync 0 0
/dev/cdrom /mnt/cdrom auto user,noauto,exec,ro 0 0
/dev/cdrom1 /mnt/cdrom1 auto user,noauto,exec,ro 0 0
/dev/hda1 /mnt/windows vfat defaults 0 0
/dev/hda2 /boot ext3 defaults 0 0
/dev/hda3 / reiserfs defaults 0 0
/dev/hda5 none swap defaults 0 0
/dev/hda6 /home reiserfs defaults 0 0
I've configured my grub with, for example,
title=Ubuntu 2.6.8 i386
kernel /vmlinuz-126.96.36.199-3-386 root=/dev/hda3
and likewise with the 686 image.
During bootup, I get an error complaining"Cannot find initrd device!" and then later it stops after saying something about unable to use resolv.conf or something like that. There are also miscellaneous errors to do with ext3 filesystems which I'll try to record next time.
Any ideas? As the chap mentioned above, trying "cannot find initrd device" gets you a googlewhack, and in French, which explains the problem but doesn't offer any advice.