I missed the Bonanza episode yesterday, and I don't have TiVo--but here's a
nine-minute clip of the opening from YouTube.  You don't get to see Mark
Twain with the Cartwrights (as I recall, Hoss doesn't think much of the pen
name), but you do get to see Howard Duff do the worst Mark Twain imitation
ever.  As in he doesn't even try...

http://www.youtube.com/watch?v=rW3dApC7zw4

John Bird