If I'm travelling and do not have access to my ISP (it's broadband, and they don't have a dial-up number), I would use whatever open wi-fi network I could find to check my email and/or minimally access the Internet. I would not access his *private* network, but would use his open WAP to access *my* network or the *public* network as unobtrusively as possible. The private network is off-limits, even if it is not secured properly.
I don't know if it is totally legal or not, but I believe it is ethical.
regards, Bob