what operating system do you use
what is your router (name and model number)
search those and find out how to properly install the router so it works.
then set it using the recommended settings from nintendowifi.com
those are:
802.11b
channel 1, 6 or 11
WEP 64/128
ssid set to public broadcast
then set up the wifi in the nds.
if you can't do it call the 1-800 number on the back of your nds and ask for free help.
-another world