The launch of the Wii this month in Australia has seem it take the crown as the best launch of a game console. According to a Nintendo newsletter:

"32,901 units sold in the first four days
Nintendo is pleased to announce that in the first four days of sale, 32,901 consumers have purchased Wii.
This means the Wii has officially broken the Australian record for the biggest launch of a video game system in history."

I can't find the equivalent figures for a comparison but the XBox 360 has sold 100,000 units in it's first 7 months.

Update: The figure for XBox 360 sales in the same period is 30,421 according to the SMH web site