Find your routers address. Usually http://192.168.0.1 or http://192.168.1.1 Type that in internet explorer, Should ask for a username and password usually Admin / Admin

Once your in find wireles security settings an set a wep key, Make sure you write it down, then that should be it... but you will need to enter the wep key into the computers that are connecting to it.

Hope that helps

Adam