Connecting the DS Lite to Internet

Question

We have a wireless internet router that works great in our house with our laptops and my Blackberry (T-Mobile). The DS can see the router, but says that the type of connection we have is not compatible with the DS. We use Comcast as our ISP and it is a cable modem. Any ideas as to how my son can connect his DS Lite to the internet so he can play his WiFi games.