You can use a range as a parameter in AR.
Model.where(:date => from..to)
Also, I'm not sure if ActiveScaffold has something to do with it. Normally, all the tasks like this one can be perfectly solved within plain ActiveRecord.
EDIT: As it turns out, author also needs to get the user's input for the boundaries. This is a common task that can be solved with one of the thouhands js plugins for datepickers. I would recommend you not to stick to ActiveScaffold for that purpose. Try this simple Jquery datepicker, and it will turn normal text field into that drop-down calendar. You will only need several lines of javascript then. If you need further advise, just ask.