This article at Gothamist has some video.

It's a three or four car train, depending on which article you
believe, running express between Times Sq and 96th streets on the 2/3
line, between 2 and 6 PM on weekends in September. The train is
authentically free of A/C.

Is this equipment that is normally at the transit museum, or is there
a cache of old trains somewhere else?

http://gothamist.com/2011/09/04/vide...k_empire_v.php