The Scientific Explorer 4200HD, I believe is a HD cable box. To know for sure, it would be best to contact your cable/sat provider to find out which box you have, and which resolutions it will support. (480i/p, 720p, 1080i/p)
Typically, companies won't issue an HD box unless you've ordered HD service. But that's just a guess on my part if you have an HD box or not.
I have a Scientific American Explorer 4200 cable box. I just purchased a Samsung led lcd 55" un8500 series tv. Do I need to get a new cable box from cablevision or can I get hdtv with this box?