Wireless keyview, as I understand, is a freeware programme/simple tool that recovers all wireless network keys (WEP/WPA) stored in your computer by the 'Wireless Zero Configuration' service of Windows XP.
If your Wireless network has not been registered on that particular PC, then no key is stored. You can't just add a wireless network to the programme.
Whichever PC you've had connected to the wireless modem/router will be the one that has the network passkey stored on it. I suggest you install the programme on that PC and run it (as an administrator). It should then "add" the wireless network and reveal the forgotten passkey.