To find your Nintendo DS's MAC address, you will need a WiFi-enabled game for the Nintendo DS. From the official Nintendo WiFi website: The MAC address of the Nintendo DS can be found by going to the Nintendo Wi-Fi Connection Setup in the game's menu. Select "Options," then "System Information." The MAC address is displayed on the top line. If you are playing a local wireless game with friends, you should not need to have your MAC address added to ResNet's list of gaming consoles.
To request access for your gaming console(s), please use the form on this page.