There are three ways to calculate a week number:
1) The first week has the first day in it and ends saturday. Then the next
   weeks are just Sundays to Saturdays. (OOPS! edited)
2) The first week starts on the 1st and ends on the 7th. This makes the 8th
   part of the second week.
3) ISO skips the first week if the first day is on a Thursday or later.
So, besides ISO, which way do you want it calculated? Sorta like "rounding".
1) The first week has the first day in it and ends saturday. Then the next
   weeks are just Sundays to Saturdays. (OOPS! edited)
2) The first week starts on the 1st and ends on the 7th. This makes the 8th
   part of the second week.
3) ISO skips the first week if the first day is on a Thursday or later.
So, besides ISO, which way do you want it calculated? Sorta like "rounding".
Get my QB demonstrator here: http://dl.dropbox.com/u/8440706/Q-Basics.zip