[Bullitt]

There's also legal liability issues to consider. If someone is using your network for illegal purposes, guess who is held accountable. I would speak at length with a lawyer before attempting this sort of thing, and having them draft up a legally binding agreement with the third party about internet usage. Could all be moot anyway, because ISP's are known to be total dicks and probably won't care if you whine "it wasn't me, honest!"