From what I heard the DS and Wii will connect (they both have wi-fi) but no software is availabe yet.
There are rumors that you will be able to transfer DS demos from the Wii to the DS. At one of our local gaming shops you can take your DS into the store and download demos that will last only as long as the unit is turned on. Maybe the Wii could act as one of theses "demo distributers"?
The DS also connects with Pokemon Battle Revolution you cans end you pokemon from your DS card to the Wii and use it as a controller it is only out in Japan but is expected to follow shortly after the release of Pokemon Diamond and Pearl