Paul,
Thanks for your comment; The sketch doesn't do anything with this class yet as it fails to compile so far. The intention is to instantiate an instance of DHT22TempHumidity which contains all the access to the dht class. I'm not really worried about hiding it, so if the dht was public that would be fine, but it doesn't seem to work like that either.
in the dht example program the dht class is instantiated by;
#include <dht.h>
dht DHT;
#define DHT11_PIN 4
#define DHT22_PIN 5
and that works fine. but when i try to instatiate a dht I get the error message
DHT22TempHumidity.h:30: error: 'dht' does not name a type
MB