Michael: What you basically want to do is to set up encryption on your network. Exactly how you do that depends a bit on the particular wireless router you have, but the basic process is to go to your router’s admin page (for mine, you go to 192.168.0.1 or 192.168.2.1 or something like that with a web browser), and then log in, and then look around for options that look like “Security” or “WEP” or “WPA” or “Encryption”. You should be able to specify a passkey (be sure to write it down or remember it!); any computer wanting to use your wireless network will then have to enter that secret key.