I don't know of any easy way other than to set up a table to correlate the actual calendar week to the week you want.
WeekTable
CalYear
CalWeek
ReqYear
ReqWeek
so you'd have something like
2002;34;2002;1
2002;35;2002;2
Then when you want to call your required week number use DatePart("ww",Date()) to find the calendar week which you then use in a query to find your required week number.
The following query would select the required Year and Week for the current date
SELECT WeekTable.ReqYear, WeekTable.ReqWeek FROM WeekTable WHERE (((WeekTable.CalYear)=Year(Date())) AND ((WeekTable.CalWeek)=DatePart("ww",Date())));