Ok- if I understand your problem you want to do this:
1. Boot from a CD running debian in live CD mode without X
2. Format the small hard drive and install Trisquel on it
3. Insert this small hard drive into the computer that can't boot from CD or
from USB
I've done this quite a few times. The directions are pretty long although you
can find directions with all the required steps do so for Ubuntu 11.04 and
use them with Trisquel (from formating the drive and setting up swap to
installing grub and the desktop).
You will have to deviate slightly in what you enter as you are install
Trisquel and not Natty (Ubuntu 11.04).
This is off the top of my head and with a quick skim of the directions
although you will need to change at least the following:
# /usr/sbin/debootstrap --arch ARCH natty /mnt/ubuntu
In the above step natty needs to be changed to Dagda (and the ARCH needs to
be i386 in your case)
You will also probably have to adjust the /etc/sources.list file for
Trisquel.
That is replace this:
deb-src http://archive.ubuntu.com/ubuntu natty main
deb http://security.ubuntu.com/ubuntu natty-security main
deb-src http://security.ubuntu.com/ubuntu natty-security main
with:
deb http://archive.trisquel.info/trisquel dagda main
deb-src http://archive.trisquel.info/trisquel dagda main
deb http://archive.trisquel.info/trisquel dagda-updates main
deb-src http://archive.trisquel.info/trisquel dagda-updates main
deb http://archive.trisquel.info/trisquel dagda-security main
deb-src http://archive.trisquel.info/trisquel dagda-security main
deb http://archive.trisquel.info/trisquel dagda-backports main
deb-src http://archive.trisquel.info/trisquel dagda-backports main
I think you can follow the kernel install instructions to find the
appropriate kernel (not positive- didn't verify).
The "sudo tasksel install ubuntu-desktop" step also needs to be changed. I'm
not sure if the trisquel equivalent is trisquel-desktop although if that
package exists it's a safe bet that it is the one you want.
If you do that you should have a fully functioning Trisquel install.
The full instructions you would need to follow are here (with the above
modifications for Trisquel):
https://help.ubuntu.com/11.04/installation-guide/i386/linux-upgrade.html
Use these directions at your own risk. The general directions will probably
work although I make no guarantees.