Type your dates into a pair of global date fields and then place these fields in the header of your report. You can even create a script that uses the dates entered in the two date fields to perform the find for you if you wish.
Another option that usually shows the same date range would be to define a pair of summary fields. Field1 would report the minimum of your date field and field 2 would report the maximum of your date field. You can then put these two fields in your header. Just be aware that these two fields won't be guaranteed to report the exact dates you specified in your find. If you enter 1/1/2011...1/31/2011 (MMDDYYYY format) as criteria, you might get 1/3/2011...1/28/2011 if the earliest record to meet your criteria was dated 1/3/2011 and the oldest was dated 1/28/2011.