Enter the start and end dates into two global date fields. Put them as merge text at the top of your report in the header:
<<globals::gDate1>> .. .<<Globals::gDate2>>
If you use a script, you can enter these two dates into the global fields and then your script can use the dates thus entered to construct the find request and perform the find. You can even pop up a custom dialog or small modal window for the user to use to enter the date range into these two fields.
Thanks again Phil.