Here's how it goes, you create a pokemon with pokegen, or similar. Must be a 5th gen pokemon. You can then upload the .pkm file and then use 126.96.36.199 for your DNS.
This does NO sanity checking on your pkm file, that's all up to you to make sure is correct.
edit: If you get a magikarp instead of what you uploaded, try reuploading. If you still do not receive the correct pokemon, you're likely not on the same connection as your DS.
Gen 4 version, by request.