During Nintendo's Fall Conference, it was announced that the Wii would be able to download and beam over DS game demos to the DS. However, according to Nintendo of America president Reggie Fils-Aime, the Wii will also be able to transfer "complete games" (meaning, not demos) straight over to the Nintendo DS.
The complete games bit isn't exactly elaborated on, so we're not sure what kind of "complete games" he is talking about. While the general assumption would be DS games, he could be talking about those rumored downloadable Game Boy games for the DS.
With Wii and DS, Nintendo Has 2 Hit Game Devices [New York Times]