Ok the only programs you'll need is Xulrunner and Chatzilla.
The requirements for Xulrunner can be found here.

The first thing you will need to do is download and extract the xulrunner to your desktop, from there open up terminal (Applications -> Accessories).
And then move the xulrunner to system location (effectively installing it)
sudo mv ~/Desktop/xulrunner /usr/share/
Then navigate to that directory in terminal
cd /usr/share/xulrunner
Then you need to register xulrunner.
./xulrunner --register-user
./xulrunner --register-global
Now comes the slightly more exciting part... Installing Chatzilla. Make sure you have downloaded chatzilla to your desktop.
sudo ./xulrunner --install-app ~/Desktop/chatzilla-0.9.76-xr.zip
Now navigate to where chatzilla has been installed.
cd /usr/lib/chatzilla
Now make everything readable and executable (because it doesn't by default).
sudo chmod a+rx *
sudo chmod a+rx *
sudo chmod a+rx chrome/icons/default/*
sudo chmod a+rx chrome/branding/*
sudo chmod a+rx defaults/preferences/*
sudo chmod a+rx extensions/*/*
Ok now obviously you'll want a shortcut to run chatzilla, one way to do this is to right click on the ubuntu logo and selecting 'edit menu' which will start 'Alacarte Menu Editor'.

Then left click on 'Internet' and then click file -> New Entry
Name: chatzilla
Note: It may come up with a 'malformed file error on 'install.rdf' but I have not found this to be an issue, so you can probably just ignore the error messege.

This how to was created with the help of: