Instructions
Turn on the DSi without any games inserted in the device's game slots. This boots up the main menu.
Open "System Settings." Various options appear.
Tap the blue arrow buttons on the screen to access page "3," indicated on the top-right corner of the screen.
Tap "Connection Settings." This is where you can set up your Internet and enter your WEP key.
Tap "None" next to a "Connection" slot to set up your connection.
Touch "Search for an Access Point." The DSi retrieves a list of available wireless Internet connections.
Tap the wireless network's name from the list. This prompts you to enter a WEP key if the network has WEP security.
Touch the "WEP" field and use the on-screen keyboard to enter the WEP key. Tap "OK."
Tap "OK" again and then tap "Save Settings."
Tap "Yes" to test the connection. The DSi connects to the WEP-secured wireless network.