You will want to reconfigure the router from a computer that is pysically attached to it. When you change the security settings and add a WEP key, the router will reboot, and you will be unable to connect to it until you have your settings on the computer updated. I would recommend that you have one computer connected with cables, and another computer connected wirelessly at the same area that you are working in. Turn on the router encryption, create a key, restart the router, and then reconfigure all the wireless clients. This way, if you mess up, you are still connected to the router.