Instructions
Click the "Wii" button in the lower-left-hand corner of the Wii's main menu.
Select "Wii Settings." This option is located on the right side of the screen.
Click the arrow on the right side of the screen.
Pick the "Internet" option.
Select any available connection option, such as "Connection 1."
Select "Wireless Connection."
Press the "Search for an Access Point" button.
Click the "Ok" button to confirm the search. This will display a list of the available wireless networks.
Select the wireless network with WEP security that you want to use. An input box will pop up asking you to enter the WEP security key.
Input the WEP security key into the text box and press the "OK" button.
Select "Save Settings."
Press the "Yes" button. The Wii will attempt to connect to the wireless network that you selected. If the WEP key was properly entered, a message will pop up indicating that you have successfully connected the Wii to the network with WEP security.