Looking back at early data... (A.k.a Super mario 64 and Sunshine on N64 and Gamecube)...
Sunshine did ~20% of the userbase. Which was (Not good) 1/5 of 4 mil is 800k lifetime.
Considering Wii will be at ~3.8 mil (Around the same as Gamecube got to in lifetime) It will launch with 15-20% of the hardware sold. With this in mind sales could vary first week from 570-760k. With it possibly reaching 1 mil 2nd week if it ends up on the higher end of my first week prediction.
I expect Wii sales to be up BIG. Expect ~150k the week Super Mario Galaxy launches and even more then 200k if they bundle the game with Wii and put in something exclusive like A Red mario Wii holder (You know, the grey thing that keeps your wii in a 15% angle) or 3 Mario stickers to customise your Wii or something.