There is a lot of confusion.
Stdreb, the Xbox with a HDMI will upconvert standard DVDs to 1080p. Standard DVDs were never recorded in 1080p, you can't just get 1080p, you have to upconvert the signal somehow. And all that is, is an interpretation by the DVD player of what all the extra pixels "should" be. As mentioned, the quality won't be the same as a true hig-def DVD. Most of those players, including Xbox or a PS3 or a standalone player, can upconvert to 1080p. Some are better then others.