If you have the record selectors property set to yes, you can select continuous blocks of records and then use Me.SelTop & Me.SelHeight in the form click event to determine which records are selected. If you want to select random records (non continuous blocks of records), you either need to add a "selected" field to one of the underlying tables or use a collection to store which records are selected. See
www.thenelson.name/#ReportFormTricks, "Select checkboxes using collection" to see how to use a collection.