from
http://doctorwhoforum.com/index.php
a great easter egg !
the Five Doctors (25th Anniversary Edition)
Disc 1
New Series Commentary
Go to Audio Options in the Special Features menu, go down to Companions Commentary and click right on your remote, you should get a green doctor who logo, click it to hear a commantary by some of the New Series Team; David Tennant, Helen Raynor and Phil Collinson