I saw this linked off a Dartmouth grad's blog. Pretty cool CSTV short about the 1940 fifth down game: http://youtube.com/watch?v=QKvefN4PmT4
(I apologize if this has been posted previously - the YouTube date is from October.)
It's even still on the first page of the "Other Sports" forum.
http://elf.elynah.com/read.php?7,100280
Then my search skills are pretty poor. I searched the database for Dartmouth, fifth down, 5th down and didn't come up with anything. I had the sense to actually dp the search, possibly remembering that I'd seen it linked here (though I'd never watched it before). Sigh.