Anyway, I'm a big fan of the film, book and even series =D
I recently did this for a friend but i'm guessing people here may also be insterested :)
This comes off the Region 4 DVD release of Watership Down. It's more of an interview documentary rather than a commentary as what's discussed is not in alignment with the film.
Martin Rosen (The director) speaks about the production of the film. I wish he spoke more about the characters and certain scenes but hey. There's still a few little interesting things in there ^^
EDIT: Fixed the 'Part 2' link.