You can follow an online tutorial and hack the Nintendo Wi-Fi adapter to connect to any device. Which means that it'll connect to homebrew as well as actual games. That's how I have mine set up.
For nesDS,
I recommend downloading nesDS WIP 1:
http://www.zshare.net/download/40030056483663/
I don't know if you'll have to dldi patch it or not, first try it without patching, then if it doesn't load, dldi patch it.
On your card, make a folder called NES, place your roms inside of it, place nesDS on the root of your card. When you launch nesDS, you should be able to select which rom you wish to play.