It's extremely likely that this will only allow viewing of the file structure. MSFT included no sort of decoder on the drive's hardware (your computer doesn't have one either) and Major Nelson commented that it took 4.7 million lines of code to get the drive to play.
Check here:
http://blogs.msdn.com/xboxteam/archive/200...rgence-day.aspx"All 6 of Xbox 360's hardware threads are hard at work while playing back an HD DVD. At the moment, the player software pushes Xbox 360 harder than any other (save, perhaps, Gears of War during some particularly busy parts of the game)."
This makes it extremely doubtful that you will be able to play HD DVD movies from this drive.