I still have the original DS and can only get online by either using WEP or no security at all. This is an annoyance since my security is set to WPA2 on my router. What type of WiFi security do each of the DS models support? I guess that also leads to another question, do certain games only work on certain types of WiFi security or is it solely based on the DS itself?
According to Nintendo's Wifi help page:
After some clarification from Micheal Madsen, it seems the answer is slightly more complicated than initially assumed. I'm basing my answer here on the connectivity section of the wiki page, and the above statement from Nintendo.
So for ease of use, WEP is the lowest common denominator. All DS models (and games!) support WEP. Use that if you don't care about the encryption protocol, and your main focus is just getting online. Things get dicey if you own a DSi or 3DS. In that case, if you want to use WPA or WPA2, the game needs to support it, as well.
I went looking for a complete list of games that would support WPA, but all I found was "Newer games that were specifically developed for the DSi will support WPA". So there's no clear way to know if your game will work or not, other than to try it.
If you don't want to downgrade your encryption protocol, an alternate option is using the wireless dongle offered by Nintendo. Be warned that it can mess with your network, though; I ran into some fun internal network issues when it was active. The only way to resolve it was to unplug it, and reboot the router.