The David Tennant Treat 4 Today is the eighth part of the Doomsday in-vision commentary. For some reason BBC Worldwide have blocked part 7!
This appeared on the Series Two DVD. All episodes of Doctor Who have a commentary on the DVD but on the Series Two DVD there were a couple where you could actually see the commentators watching the episode.
In this video it is David Tennant and Billie Piper who are watching Doomsday.