In the suppression formula for all sections in your subreport, for all sections that contain only data, turn on "Suppress Blank Section." Fo sections where your've typed text, put something like "IsNull({table.some_key_field})" using a field from your data that determines whether there is data in the subreport.
In the main report section where the subreport is located, turn on "Suppress Blank Section".
-Dell