Instructions
Tap the wrench-shaped "System Settings" icon on the bottom of the Nintendo DSi's main menu.
Tap the right arrow twice, then tap the "Internet" button.
Tap the "Connection Settings" button.
Tap one of the buttons labeled "None" to create a new wireless connection.
Click the "Search for an Access Point" button to scan for a signal from nearby wireless routers.
Tap the name of the wireless router that you want to connect to. The router should have an icon of a gold padlock -- locked or unlocked -- next to it. If the router has an icon of a silver padlock, tap "Back," "Advanced Setup" and one of the "None" buttons.
Tap the "Change Security Settings" button and enter the encryption key for your wireless router. Tap the "OK" button when you are done. If the router's name had an unlocked padlock icon next to it, skip this step.
Tap the "OK" button.
Tap the "Save Settings" button.
Tap "Yes."