Hi,
You don't need to base it on a form, you can get the data information directly from the query as follows:
Now I am assuming that you have two fields one known as your FirstDate and the other known as your LastDate in your query. I also assume that you have in the criteria below each field something like [Enter First Date] and [Enter Last Date], which prompts for the date range you require.
Now in the report create two unbound text boxes and name them FirstDate and LastDate, in the source section of the properties for each of these boxes type in [Enter First Date] and [Enter Last Date], save your report and run it, now each time your run that report the dates you specified will appear in your report where you have positioned these unbound text boxes.
I know it works because I do that currently with some of my reports.
good luck.
John