Not a lot of explaining necessary here . . .
Sophia Loren, Audrey Hepburn, and most recently, in the December Paris Vogue, Lara Stone demonstrate how to work a wimple.
Call me crazy, but I think Nicolas Ghesquière at Balenciaga is going for much the same effect from an entirely different direction, with his sleeveless hoodies for Spring 2010. Yes they're black leather rather than starched linen, and owe as much to the hood rat as they do to the lamb of God, but don't they make the wearer look alluringly untouchable--encased--in exactly the same sort of way?
Audrey Hepburn in The Nun's Story, Sophia Loren in White Sister, Lara Stone photographed by Cédric Buchet for December 2009 Vogue Paris.