window washers. These empty figures seem to be a theme of hers.
The building itself was designed by the Philip Johnson/Alan Ritchie architecture firm. They have a brief description of the project with images of the whole building.
Update (Oct 2008): Since I first posted this Muriel Castanis died. Her Obituary is in the Nov 2006 New York Times and the LA Times did a story on the statues in Jan 2007.
Update (May 2009): I was contacted by someone in New York who has a 4 foot hanging ghost sculpture by Muriel Castanis for sale. If you are interested, contact me (my email is at the right) and I will pass your interest on.