I would look up WeekDay or DayOfWeek in the Crystal Help to get a start. You would have to perform logic in your report to determine the date range and then you could update an array and limit the records to those that have dates in the range (or you could just use and if statement instead of the array).
Or you could use a stored proc as a datasource and do the filtering there. I don't know off-hand, but I am sure that there is a WeekDay function there as well (or something similar)
I realize that you have probably found a solution by now.