Your HD quest will be long and hard... on digital cable. Unless the cable provider specifically states that they carry a HD signal forget it. Here in the SF bay area we have 8 digital stations. Not all broadcast an HD signal but the majors do (ABC, CBS, NBC, PBS). And all you have to do to receive them is have a HD STB and an outside over the air (OTA) antenna. And from looking at online data you have 9 digital channels that you should be able to receive with an OTA antenna. Go to www.antennaweb.org
to check out what you would need. If you do get an HD STB with satellite you would then have access to HBO HD and depending on which DBS service you get you would have access to Showtime HD, HDNet and PPV HD. It will be some time before satellite carries local HD channels due the bandwidth required to carry said signal. E* does offer CBS HD but only in special areas and you may have to get a wavier from the local CBS station (good luck getting it). There are no other "local channels" being carried by satellite today or the foreseeable future.
When you asked if set up boxes are read writable? Are you referring to the Set Top Box (STB)? If so, there are no read/writable boxes that I know of. If you are referring to STB that can be bypassed - we don't talk about that here.