most likely you did not secure your router properly. Go back into the router and go through the wizard. It will take you through the entire process to secure your network. Once done, you will have to remember that key.
Also, the other ips are likely some people using your wireless signal. Identify your ip address and then you can revoke the other addresses.
First, secure your network, second connect using your WEP, WPA, or WPA 2 key. That alone should kick any unwanted users of your network.