Another technical note: I was having problems connecting a Nintendo DS to the WFC, via an Airport Express, for playing Mario Kart online. The connection kept dropping out after about 5 minutes, giving an error message and freezing the machine. I found that connecting a laptop to the ethernet and sharing its connection via Airport, as per this hint, fixed all the connection problems.
(if anyone wants a game, my code is 287 826 668 421, though I'm not online very often)