Network setup is almost always a bitch.
Computer:
First, I'll assume you're using Windows XP. Connect your computer to the router, either by plugging in a cable from your computer to one of the ports (not the WLAN port) on the back of the router or by connecting with a wireless USB adapter.
Check the 'status' of your connection, to find your computer's IP address (You'll need to enter that at the IP prompt on DS2Win).
Make sure Win2DS is running on your computer.
Router:
Make sure your router is able to transmit with wireless B. If you have it set to G-only (or N, if you have it), it won't work.
You may want to set up a WEP key. Make sure it's 'Open', and not 'Shared'.
DS:
You should have run an online-capable DS game (or DSOrganize, etc.) to set up your connection.
Enter the SSID and WEP key (if applicable) of your router
The Gateway and the Secondary DNS will both be your router's IP
The primary DNS will be your computer's IP
Make sure your DS's IP doesn't conflict with those.