It is reporting that you have a network card that is not connected to another PC (or router, etc). This could be a true network card (in an expansion slot or built in to the motherboard), or a Firewire port (e.g. on a Creative Audigy soundcard).
To disable the icon, right-click it and choose Open Network Connections. Then just right-click the network connection, choose Properties, and tick the 'show icon in notification area.....' box. If it is not going to be used, you may as well right-click the network connection and choose Disable. You can always re-enable it later if you need to use t.