lesto
As far as i understand the I2C bus sytem is based on an open collector arrangement.
This enables any device to communicate.
The pullups should be fitted between SDA (A4) and 3v3, and SCL (A5) and 3v3 (on a 328 Arduino).
Note this reference uses 5v, but a Wii uses 3v3.....
Communication between the MP and NC should be sorted within the MP, so you shouldn't need any others.
Mark