It was quite easy in the end, I nearly kicked myself for not thinking
about it sooner.
Using another PC I wrote an Ubuntu live CD to USB key, I then copied
the ChromeOS-Vanilla-0.8.71.2010_09_21_1226-rdb7d4e77.img file to it.
I haven't tried the very latest build yet.
I then I booted the Ubuntu live environment from the USB key on the
EEE. Press ESC at the BIOS screen and select the USB key to boot
from.
Once in Ubuntu I then wrote the IMG file to the second SSD using DD as
follows:
sudo dd if=/cdrom/ChromeOS-Vanilla-0.8.71.2010_09_21_1226-
rdb7d4e77.img of=/dev/sdb bs=4096
I then rebooted, hit ESC again and selected the 2nd SSD to boot from
and it successfully boots Vanilla.
Notes:
* You will want to check where the USB key root is mounted, for Ubuntu
it was the /cdrom folder, this is where the image file will reside.
* Also you will want to double-check Ubuntu is seeing your second SSD
at /dev/sdb, if it is not then you will want to check the hard disk
order in the BIOS.
* Pretty much any live CD that includes DD should do the job fine.
* I haven't tried it, but it is possible that just writing the IMG to
the USB and making the USB key the second boot device may also work,
rather than having to write it to a local SSD, I am not sure if Linux
will force IDE & SATA disks before USB disks in device ordering or if
it just uses BIOS ordering.