You can acess your router (usually) by typing
http://192.168.1.1 into your internet adress bar.
You might then have to enter a username and password that you assigned during setup. (not the ntl ones)
Then you should be presented with a menu (I'm not sure what it'll look like as I don't have a belkin)
This menu should have a wireless section, or wireless security (tabs within tabs if you get me)
The best securtity to use is WPA, it probably stands for something but I don't know what. You'll have to put in a password or something which is converted into a hex key, which you then enter when you click to connect on the net.
Your pc should remember this hex for whenever you go online.
EDIT ; Changed the adress to access router.