Excuse my ignorance, but I have a question regarding older movies now seen on HD-DVD, such as Robin Hood and Casablanca.

These older movies were not shot in HD, so how can they now be on HD-DVD? What I mean is, how can they be considered truly Hi-Def if the originals were not even shot with Hi-Def cameras?

Also, on a related note, I've noticed that DirectTV added quite a few HD channels such as TBS HD. Many more to come such as Food Network HD. Will these all just be "upconverted 480" material like TNT HD? Meaning, will they be "True" HD or just upconverted garbage? These channels are nonsense if they won't be true HD, IMO.

from what i understand, film has much higher resolution than 1080p, so they can simply make a digital transfer of it and then re-encode it to 1080p.

not only are the older films you mention not shot in HD, most films today were not shot in HD but on film.

Ahhh, so if it's shot on film, releasing it in HD is not a problem.

Ok, how about the new HD channels that are popping up. I'm assuming that they won't be truly Hi-Def, just upconverted SD material that looks like crap (like TNT HD). Is that a correct assumption?

For great examples of how good older films can look on HD, check out "Grand Prix" and "Smokey and the Bandit". Fantastic transfers that look as good as the day they were released.

Yes - some of the new HD channels still use some upscaled SD material - but this is not related to what you'll see on HD DVD (or Bluray).

Per the above.

Film can have higher than 1080p resolution. Now since over 90% of films are still shot on film and not HD Cameras, the mastering process from film to digital HD has been used for many years now.

For some examples see the links below:

Adventures of Robin Hood (1938)
http://www.hdmovies.co.nz/hddvd.php?id=Adventures%20of%20Robin%20Hood

Forbidden Planet (1956)
http://www.hdmovies.co.nz/hddvd.php?id=Forbidden%20Planet

The Searchers (1956)
http://www.hdmovies.co.nz/hddvd.php?id=The%20Searchers

Grand Prix (1966)
http://www.hdmovies.co.nz/hddvd.php?id=Grand%20Prix

Compare them to your favourite films here to get an idea of relative quality:
http://www.hdmovies.co.nz/screenshots.php

Yes, TNT HD older shows are just upconverted SD or at 480i, (old Law and Order) but any newer HD shows (recent Law and Order) will be in HD. This is true for any HD station, PBS, A&E, CBS, ABC, etc. If TNT wasn't HD, then the new shows would just be 480i (like CSI on Spike channel).