Depends on how they are recieved in Japan really. Kirby games on the NES / SNES / GB / GBA / DS were huge in Japan...N64 / GC not so much. Donkey Kong was huge on NES / SNES.
1.5m-2.5m seems about right for Kirby's Epic Yarn. I'm going to go with 6-7m for Donkey Kong though. Could be bigger - the original Donkey Kong Country did almost 10m on SNES I believe, and alot of Nintendo's franchises on Wii that have been given social elements (Mario Kart, Super Mario Bros, Smash Bros., Mario Party, probably others) have grown by leaps and bounds over previous titles for NES / SNES / N64 / GC.
There are a ton of million-sellers (at least potentially) arriving later this year for Wii though, so timing may be somewhat important too.
People are difficult to govern because they have too much knowledge.
When there are more laws, there are more criminals.
- Lao Tzu