SSAS Time Dimension

I have made a server time dimension. I am using only the ReportingYear,
ReportingMonth, ReportingWeek, Date. I am using the Weeks544 and the week is
starting on sunday. The problem is that week 1 in 2008 starts on sunday 6th
january which is wrong, it should start on sunday 30th december 2007.
So the Hieracy should look like this:
-2008
--January
---Week1
----Sunday 30th December 2007
----Monday 31th December 2007
----Thuesday 1st January 2008
---- etc

It is on a SSAS 2005

I was under the assumption that the first week of the year was the one with
thursday in it.

Anyone know how I can change this? without making my own source dimension
table.