You'll have to edit the selection formula.
1. Go to the Select Expert.
2. If nothing has been added for criteria yet, select the date field you want to use.
3. Click on Show Formula.
4. Edit the formula to be something like this:
{MyTable.DateField} >= CurrentDate - 7 and {MyTable.DateField} < CurrentDate
You may have to tweak the comparison (">=" to just ">" and "<" to "<=") to get the exact days that you need.
-Dell