Instructions
Turn on your Nintendo DSi and tap the wrench icon at the bottom of the screen. The System Settings page will then appear.
Tap the "Internet" option and then tap the "Connection Settings" option. Tap the "Manual Connection" option.
Enter your network name into the gray box by using your stylus pen. Tap the "OK" button and then tap the green arrow button until you get to the "Security" page.
Select the "Change Security Settings" option and then tap the "WPA-PSK (TKIP)" option. You will then access the WPA screen.
Enter your WPA password into the text box and then tap the "OK" button. Tap the "Save" option and your settings will be saved.