you can add the field to the form on the search page using the Dreamweaver insert menu, Insert -> Form
then on the results page, go to the bindings panel and make sure there is a binding group for the form from the search page, if there is not a binding group for the search form, click the plus button then Select Form Data. Click the folder icon in the form data wizard and select the search page.
no on the server behaviors panel, double click the data assist search server behavior, create your new search criteria by clicking the plus button, if you need more details on the options in the criteria settings, click the help button.
