Got the kids a pair of Nintendo DS Lites, and after a few days, they got around to playing with the WiFi that's built into them. And of course, they didn't work with my wireless setup. Fortunately, the fix was relatively straightforward (eventually).
Both the original Nintendo DS and the newer DS Lite have built in WiFi. The problem I ran into though was that my AirPort Extreme was set to use WPA encryption, not the lesser (and more easily hacked) WEP encryption, which also required the rather ugly 13 character passphrase. I did test briefly using WEP here, but the thought of having to enter that 13 character phrase on every WiFi enabled device in the house (multiple laptops, multiple desktops w/WiFi, a pair of iPhones, the two DSs), plus having to do this for any guest systems just made this totally unattractive. So, in the end, I decided to set the wireless security to None.
However, all is not lost! I decided to use the old fallback, MAC Address Access Control. Basically, this involved me adding the MAC address for each device to the Access List on the AirPort Extreme, most every modern router will have a similar feature. With the AirPort, I was able to go to the Advanced settings and view the log of connections, so I just fired up an internet connection on all my devices (took a few minutes of going around the house and firing these up one at a time), then going back and copying the MAC addresses out of the log entries, and giving each a description for the device (important to remember the order used!), and in about 10 minutes I was done.
As a last step, I changed the Default setting to disallow access, so that only devices specifically listed will have wireless access. The down side is that any guest systems will need to be specifically added, or have the Default reset to allow access temporarily, either should work just fine.