WS wrote:
Weeknum does not show 53 for the entire week of 12/28/08-1/3/09, it shows
week 53 for 12/28-12/31, and week 1 for 1/4-1/3/2008. The week number can't
be both 53 and 1

You could use something like this, which pulls the WEEKNUM for every day from
the preceding Sunday:

=WEEKNUM(A1-WEEKDAY(A1)+1)

Keep in mind that there will be no week number 1 for any year that doesn't start
on Sunday.