Using kismet, if you sit there long enough you will get a valid IP off of the network. So, changing the IP means nothing.
@goku2100, I don't understand your response about the invalid line. You can type in whatever you want, and then "cloak" the access point. All this does is keep the access point from broadcasting the SSID to make it easier for clients to find it. However, while it isn't being freely broadcasted it *can* be found when a client negotiates its connection with the WAP. If someone is sniffing the connection, it will pick up the name of it (however, by then it will probably have the MAC, which is first, and then the IP of the WAP). If you can, switch to WPA as soon as possible to protect yourself. In addition, if using preshared key, use a minimum of 20 characters for the key. The newest thing is to guess the keys used in WPA-PSK rather than directly breaking the encryption. If you use a strong key (>20 characters with mixed case and symbols) you should be set.