I'm probably about to buy either a Hitachi 55PMA550E or a Pioneer PDP504HDE, and feeding it with a Sky+ box or a DVD player. Would I benefit from buying a scaler? (I'm not actually sure exactly what a scaler does, but I'm assuming it does a high quality conversion of the incoming stream to the plasma's native format e.g. 768p). I don't have more than a few hundred quid to spend, so I can't go for an expensive one.