There is nothing for you to do unless talking with your neighbor and ask him to grant you access, otherwise just start talking to them and ask for the username and password....
It is actually fairly easy to break WEP authentication. FBI demonstrated it a few years back at a blackhat event. It took them about 3 minutes.
Just remember it is considered illegal to use a wireless connection that has authentication and if they know what they are doing they can tell if you are on it and even steal your data ;).
