In the Criteria of an appropriate Date field put something like
Between Date() -7 and Now()
Now if you need the last calendar week, it gets a little more complicated.
Something like below will almost work; however it will probably bomb out
during the first week of January.
SELECT tblDates.wa_date,
DatePart('ww',[wa_date]) AS TheWeek,
Year([wa_date]) AS TheYear
FROM tblDates
WHERE (((DatePart('ww',[wa_date]))=DatePart('ww',Date())-1)
AND ((Year([wa_date]))=Year(Date())));