Since the Nintendo DSi and Nintendo 3DS are compatible with WPA security, can I play Nintendo DS games online using WPA?
Nintendo DS Game Cards are only compatible with WEP security, and are not compatible with WPA security. So while you can enjoy other online features of the Nintendo DSi and Nintendo 3DS with WPA security, you cannot play Nintendo DS games online with any system if your network is secured with WPA.
Taken directly from the Nintendo website.