I'm not sure what that response from Orange is on about, regarding the WEP key, TBH. The other part just seems to say that the LiveBox has a range of 100ft, and anyone in that range can potentially connect to it. However, as I said before, you need the MAC number to connect so you should be safe from unauthorized access. :)
BTW big10p, did you get you MarioKart DS working online ok?
I haven't gotten around to trying yet, TBH. Also, for some reason, I can never get on the Nintendo Wi-fi site which is supposed to have info about how to connect using a LiveBox, I believe.