[dad911]

If you are using wifi, any computer connected, even wired, is still on network.

For example my printer and server are connected via cat5 wire, no wireless, but I can still access them from a wireless laptop.

There are certain things you can (and should) do. Off the top of my head:

1) Change default router passwords and names.
2) stop broadcasting your network name.
3) Turn off 'guest' wireless.
4) Some providers (I know comcast did) broadcast a 'provider' connection, so other customers can actually access internet through your router. It isn't easy, but turn that off.