Microsoft and Toshiba showed off their HD DVD drive for the Xbox 360 at IFA 2006. No video demonstration or life usage, but starting halfway in the video, you can get a 360 degree view of the drive. There's two USB ports on the back of the drive, one standard and one small one—most likely one USB A and one USB B. This gives you a better look at the actual dimensions of the drive, which is about as thick and long as the 360, but not as tall.
Toshiba HD DVD [IFA2006]