Obtain a FAT formatted mini SD card.
  I don't think it matters if it's fat16 or fat32, but 2GB or less is best.
Obtain IZ2S205beta-enhanced-020410.zip from here:
  http://russelldavis.org/2010/10/21/proper-release-of-iz2s-enhanced/
Unzip the IZ2S zip file onto to the root of the mini SD card.
Copy iz2jffs-e5.10.tgz to the root of the mini SD card.

Boot IZ2S:
  Skip the wifi setup.
  If first time running IZ2S wait for it to generate keys.

At command prompt type:
  cd /mnt/ffs
  mkdir /mnt/sd0/backup
  cp -R * /mnt/sd0/backup/
  sync
  sync
  rm *.arl
  rm *.xml
  rm -rf wpa_supplicant
  rm *.jpg
  rm Z*
  sync
  sync
  ls

You should have only properties.txt and start.sh left.

  /mnt/sd0/bin/busybox tar -xzvf /mnt/sd0/iz2jffs-e5.10.tgz
  sync
  sync
  df -h
  poweroff

Wait for screen to go black.
Remove IZ2S sd card.
Press the green button.
Answer questions until you get a command prompt.  Then type:

  gmenu

For some reason i didn't get connected with wifi the first time, but it did connect after a reboot.  I'm keeping an eye on that.

Also the /mnt/ffs/start.sh in some (older?) version of the stock firmware appears to run Zipit2 instead of Zcovery.  This results in the zipit booting only to the logo screen.  You may want to copy this start.sh to /mnt/ffs/start.sh if your zipit does that.

http://prototypeur.free.fr/start.sh