I dont know what my network key is. - Linksys Wireless-G WRT54G Router

Open new Internet Explorer and type in address Bar " http://192.168.1.1" and hit enter.
Leave user name field blank and type "admin" for the password.If you changed the router password, then log in using your password to login to the router.
Once you are in the router setup page, click on the Wireless Tab at the very top of the page. Once you are in the Wireless Tab, just right under the word Wireless you click the sub tab that Wireless Security. On this page you will see the Security Mode. If your security mode is set to WEP you will have four sets of keys available. To known which key to use look for the Default Transmit (Tx) Key, If your default transmit key is set to 1, then you will use the key in Network key 1 to connect to the wireless network. Now if your Security mode is set to WPA (Personal/Pres-Shared Key/PSK) what's inside the WPA-shared key or Pass phrase / Personal Key box is the network key for your wireless network.