Hi,
Easiest thing to do is to set up MAC Address filtering on your router.
Every network card has a unique MAC address and by turning on the filtering means that you only allow network cards that you specify to connect.
To find out the MAC address of your network card, open a DOS prompt (Start - Run - CMD) and then type IPCONFIG /ALL
You should see an entry like:
Physical Address. . . . . . . . . : 00-11-0A-A3-88-38 <obviously different for you>
You may see information for more than one network card (an onboard network card and a wireless one. Add both into your router config.
Take a look at your router manual on how to use this feature, or post the make/model here and I can help further.
Regards,