I'd definitely try the Nintendo forums.
Otherwise, I'd tests some stuff. Disconnect computers from router, so you won't have people messing while testing. Then go into router menu and remove all security and the like. Try to connect with nothing enabled. If that works, start adding in your security features. I'd also make sure your modem is turned on. I turned off my modem without thinking and started getting errors wondering what was wrong. So check all the idiots/simple stuff first. Make sure your WEP keys are matched up correctly.