Automatic partitioning on Ubuntu 7.04

[J David Eisenberg]

Here is my ks.cfg file (comment lines removed to save space; blank
lines added for readability)
#====================
keyboard us
mouse
timezone --utc America/Los_Angeles
rootpw --disabled
user superuser --fullname "Super User" --iscrypted --password
$1$tqSDxdlI$Im7dQsfbZoJtzLIUaoUKG0
reboot
text
install
url --url http://192.168.0.1/ubuntu
bootloader --location=mbr
zerombr yes

clearpart --linux --initlabel
part swap --size 500
part /home --fstype ext3 --size 3500
part /usr/local --fstype ext3 --size 2500
part / --fstype ext3 --size 8000

auth  --useshadow  --enablemd5
firewall --disabled
xconfig --depth=16 --resolution=800x600 --defaultdesktop=GNOME --startxonboot
%packages
@ ubuntu-desktop
#=============================
I'm using the alternate install CD, and put this at the beginning of
the boot prompt:

ks=http://192.168.0.1/ubuntu/ks.cfg

Everything goes well until partitioning; at that point, the
partitioner asks me how I would like to proceed. If I say "manual
partition", it responds with "No root file system is defined."

I am doing something stupid here, but can't figure out what it is.
Assistance would be greatly appreciated.