For the following example, I am querying a table with three fields: "FName", "LName", and "Date".
The query's SQL syntax would be:
SELECT Table1.FName, Table1.LName, Table1.Date
FROM Table1
WHERE (((Table1.Date) Between [StartDate] And [EndDate]));
Then, I place a text box in the report header, and set the text box's Control Source property to:
="between " & [StartDate] & " and " & [EndDate]
That should do it!