HD DVD movies on DVD-5's and DVD-9's???

Are you talking about movies or calibration material?

For calibration the size of the disc fits on a standard DVD.

For movies it is probably just a re-encoded/compressed version.

Correct.

In theory an H.264 re-encode of an HD disc should be better quality than a DVD of the same size since the encoding efficiency is better.

Of course this is possible. It’s officially called “3x DVD” for HD DVD and “BD9” for Blu-ray. It’s meant for cheap production of documentaries and short films. It allows for about one and a half hours at high quality 1080p video.

You're thinking of these bit rates incorrectly. You have to separate the concept between the encoded bitrate and the transfer rate that a medium can provide.

With DVDs, MPEG2 compression is used and is at around 8mbps (as you said). With HD-DVDs, VC1, H264, or MPEG2 is used with bit rates as high as 40mbps (as you also said). So, we have established that these are data rates.

Since a DVD is merely a disc with some data on it, we can put anything we want on it. This includes movies authored as DVD, HD-DVD, and even Blu-Ray. The medium just needs to provide enough bandwidth for the movie to play smoothly. A DVD drive reading at 4x or higher should be able to provide 40mbps for data transfer. Or, if you authored a small amount of HD material that can fit on a CD, you need a CD drive that can provide at least 36x speed.

I'm not sure what you're getting at. Are you referring to HD movies being released on standard DVDs? You can create your own HD-DVDs using standard DVD-R discs and your existing DVD burner using the process outlined in the HD DVD software section of these forums. I've been making my own HD-DVDs of shows recorded on my HTPC and my S3 Tivo for about a year now and the results look as good as the original HD broadcast. They also have DD audio soundtracks. The one caveat is that most movies have to be split up into multiple discs.

Use a drive that spins faster than 1x. Most DVD-ROMs today can spin at 12-16x, which gives you more than enough maximum bandwidth.

On a re-encoded disc you won't be getting 40Mbps off the disc.

Yes. This is correct - but this is a limitation brought by the material on the disc. Is is not a limitation brought by the DVD drive/media/ and red laser. That is where the OP is confused.

All that it takes to make a HD DDVD is actually just a readable disk with a particular file structure. There is nothing that requires it to be at a particular bit rate. Put another way, any of the HDTV shows you watch on TV have a bitrate between 10 and 18 Mbps . Sadly, this passes for HDTV these days. If you can record these shows on your computer, you can easily create a HD DVD on a DVD that contains an hour long show.

I do it all the time when I want to timeshift on evenings there are too many shows all on at the same time.