I don't see anything wrong with that sentence other than it might be a little unclear as to when the '6th week of 2009' actually is! Did you mean the first week of February? This might make it a little easier to understand.
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AvangiI don't think it's natural to count the number of weeks from the beginning of the year. I don't think anyone in the US would have any idea which week it is, without stopping to figure it out. However, in certain industries, perhaps that kind of reckoning is useful.