So far all attempts to use MKVmerge GUI resulted in files with no audio. I'm completely lost on how to use eac3to. I have been able to backup the HD DVDs to BD-Rs using AnyDVD to rip the disc. PowerDVD 7.x will play the BD-R copies. ...and the blank 25GB BD-Rs cost me less than $3 each. So far, every HD DVD I've bought fits on a 25GB BD-R. My trial period has ended and I can't afford to buy AnyDVD until next payday - or later because of other plans, but this is the only way I know to successfully backup HD DVDs at the moment. I've been focusing on the HD DVDs that show no sign of a Blu-Ray release soon.
I'd love to see easier to understand instructions for ripping HD DVDs to a format I can convert. MakeMVK won't rip any of the HD DVDs I have. ...at least not the movie itself.
Check the slysoft forums for a frontend GUI called Clown_BD (current version is .64). Or just BING or Google it. (it comes right up).
I've done all my HD-DVD's with it. Very easy to use as a layman.
EDIT: Clown_BD will do it lossless. If you want a tool to shrink the HDDVD's, another option is Ripbot264. Ripbot however will take a long, long, long time and will peg your CPU to 100% regardless of horsies under your hood.