OK a few things...
Thax: Bill Gates stated that they were considering a HD-DVD player for the xbox.
Now to the HD-DVD question, HD-DVD and BR-DVD are both formats for a disc. Just as CD and DVD discs are. HD-DVD just means that basically the format of the disc is different, but it will still carry the same information that you could find on a DVD. Now, HD-DVD can carry high-definition video that would probably be displayed in 1080i or 720p, however if you had a standard definition TV then it would most likely scale down the resolution so that you can view it.