I'm not sure how soon your router will "like" Nintendo DS wireless. From what I've read, there are very few routers the DS wireless DOES like. This might be intentional on Nintendo's part, as you can shell out $30-40 for a Nintendo USB wireless router thing (I don't think that's the technical name for it, though) that is supposed to work just great. Kind of a cheap trick, but nothing consoles haven't done to us before.
As a sidenote, I read an article on Gamespot today that said that Mariokart wireless was having trouble with interference from microwaves, other computers and the like. That's a problem I think they'll be able to fix soon--but for now they have the genius idea of turning your microwave and computer off . . .
(And once I get my copy of Mariokart, I'm looking forward to going out in the world and proving my skills as a player. I'll post my "friends" code here so that people can try to beat me. Go ahead. I double dog dare you.)