Didn't know craig had confirmed, good stuff!
As for how its all going to work -- I think DS will function on any wireless open network. Its possible that there could be options or a kind of wizard for configuring in secure environments (although Iwata's speech re: WEP etc puts that in doubt).
For those who have standard ethernet connections, if they really wanted to get serious, Nintendo could even release a no frills PCI, USB or Firewire peripheral for PCs.... or a third party could jump in and do it instead.
People have already got DS downloading code from PCs using "DS download" option and various PCI cards with a common chipset. Perhaps something similar could be done on an official basis for an affordable one off price.
The Gamespy technology sounds awesome. A lot of games on consoles have used some element of the Gamespy middleware before, but Gamespy have never really backed a whole console with it before... I'd say some features are gonna be able to come as standard in most DS online games. I don't wanna jump the gun but there is hope here for their voice chat systems, leaderboards, file downloads/trading, and new things like online pictochat, gamertags etc to make it into the fray and be a common occurance.