DATEPART(ww,Date) with SET DATEFIRST

I´m using SQL Server 2005

I´m trying to get the week with DatePart(ww,date) function

My code

SELECT datepart(ww,'2012-01-08 00:00:00')

Return 2

But I want ...

Return 1

According with IS0-8601 and this table from this website

YEAR 2012 Week-01 From 2012-1-2 to 2012-1-8 ...

Am I wrong?

There is any trick with SET DATEFIRST 1, I´m trying without success.

Thanks for your time