How to setup a 4axis gantry plasma machine using gmoccapy?

No, I don't use ethernet-controlled motion control hardware. Indeed I boot the RTAI kernel image. I'll make a new install as you said. I hope it works. Thanks for giving help, andy.

With a fresh liveCD install, check that LinuxCNC works, then once that is going we can look at updating to 2.8

I made a new install using the LiveCD. Linuxcnc is a live and working.

OK, so, to get 2.8: (I will try to describe the GUI way).
System->Synaptic Package Manager
Settings-Repositories
(TAB)Other Software -> (Button)Add
Put in (as suggested by the buildbot at buildbot.linuxcnc.org)
deb buildbot.linuxcnc.org/ wheezy master-rt
Click "Add"
Now, close the dialog and press the "reload" button in Synaptic
There will be a complaint about keys. I think you can actually ignore that for the moment.
Now click the "search" button and look for linuxCNC. You should see a version 1:2.8.0_ja....
Select and install that.

I received an error message because Synaptic added it without the http prefix, so I edited it from terminal. Now, the Linuxcnc 2.8.0_ja is installed.

emad@Control:~$ linuxcnc
LINUXCNC - 2.8.0-pre1-2765-g5fec8d9