The process of converting your HD DVDs to Blu-ray is time-consuming, potentially costly and sucks balls. Really, there's almost no reason to, since you can bet most everything on HD DVD will be released on Blu, and if you have a million HD DVDs you don't wanna rebuy, you should just buy a dual format player. But if you revel in pain, here's how to do it, thanks to the crazy video guys at Doom9.
First, get an HD DVD ripper—DVD Fab HD Decrypter is free—and rip them. Now it gets messy.
EVOdemux will "demultiplex" the files, after which you need H264Info or vc1conv (v0.2), depending on which one you ripped in. Then use eac3to to cram the audio enough to fit on a 25GB Blu-ray disc. TsRemux or tsMuxeR will get your video ready to burn. You can burn it onto Blu-ray discs with either IMGBurn 2.4 (free) or Nero 8 ($100, plz), but you obviously need a BR burner, which is a few hundred bucks, at least. Finally, punch yourself in the face. [Doom 9via Wired Wiki ]