Having watched some more DVD's where the picture quality is the dogs

and also watching some more SKY, I have been compelled to come back again and ask some more stupid questions
I've had my SKY box for a while now. Would the picture quality improve if I got a newer one? I was wondering if although the signal strength is ok, what about if the box cannot decode it fast enough? Is this possible.
Does anyone else box get really hot? I've got plenty of ventilation around it and it still seems to get really hot on the top.
EDIT - Would the scart lead i use also make a difference to pixellation?
ta