How to secure wireless networks?
In this easy to understand article, John Laster describes ten different technologies used to secure wireless networks. A lot of these can be extended to wired networks.
Most of those technologies can be implemented at home to secure wireless networks. The most commonly used should be WPA2-PSK. I would not recommend using WEP as it would be too easy for amateur hackers to crack.
Remember that you are legally responsible for the action of the users on your network.
Using WPA/WPA2