base your form on a query. add criteria to the StartDate or EndDate field
(whichever you want to base the selection on), as
=>Date()-7
be careful when using Now(), because that is very specific to "this minute
and this second", rather than just "this date". if your date/time fields are
populated with date and specific time values, then getting all the records
for specific *date* ranges (irregardless of time) takes a little more work -
so i won't go into that unless you need it.
hth