(
Original question)
From what I understand, you have a Livebox thingy, which gives you a wifi signal. And I assume that you have a cable from the Livebox to your main PC.
So, you need to set up the wifi with the Livebox, if it isn't already. How to do this, I'm not sure. I would assume that it came with some instructions, but I really don't know.
Once the wifi is activated, then you can (assuming your Powerbook has an airport card already) connect to the internet as it says
here and
here.