Last year there was (essentially) 9 weeks which represented the holiday boost for the Wii:
VGChartz Hardware data for the period 10th Nov 2007 to 05th Jan 2008:
Console | Wii |
Total
|
6,138,794
|
All things considered, I wouldn't be too surprised to see Nintendo sell 1/5 to 1/3 more units in 2008 than they did in 2007 which would work out to 7.25 to 8 Million units sold over the Christmas 2008 holiday season.