I'm really not to savvy on the details of the Wi-Fi for the DS, I just know that the Wii's Wi-Fi capabilities are super awesome.
I do know, however, that in order to access the Nintendo Wi-Fi connection, you need a Nintendo Wi-Fi LAN Adapter or a Nintendo Wi-Fi USB Connector. If you're in need of either, simply go to Best Buy or somewhere and ask for one, I'm sure they have them. It might not be a bad idea to also ask the tech guys at Best Buy or somewhere if they know how to help you with your Wi-Fi Connection, that or I'm sure if you dig on the Nintendo website you'll find something.
Hope this helps! And enjoy Diamond, it's a great game!