hd dvd max bitrate is 29.4 mbps, bluray is 40mbps, but i bet u cant tell the visual difference between them unless one of them were badly "mastered".

Dont forget hd dvd/blueray playback on pc still need directx hardware acceleration(DXVA) eg nVidia purevideo, and ATi Avivo,
both also need external software player to works(only for h264 iirc) eg powerdvd or nero 7 ultra edition.

Coreavc is another choice, which is "cracked" and distributed on some codec pack already
our opensource Hero(ffmpeg) is still too slow for this

asus should make one that support both hd-dvd and blueray one
save money/space/time/electicity