You can substitute dumbbells for barbells (they are both "weights") in any workout. Cathe will often mention this in her more recent workouts. THough barbells might be easier to use and more comfortable for squats, for example, you can use dumbbells there alo. One workout that uses just dumbbells "as-is" is PUB. PLB uses a barbell, but Cathe even mentions that you can use dumbbells instead, and quite a few people seem to, to make changing weights easier and faster.
There are actually advantages to using dumbbells instead of a barbell for upper body work: your stabilizing muscles get more of a workout because they have to help keep the weights in balance; your strong side can't compensate for your week side, the way it can when you use a barbell; and with some exercise--ie: shoulder presses--using dumbbells allow you to change your grip slightly to find a position that may fit you better, and be kinder to your body ---in this case, the shoulders.
