Night Dresses

Where can I rent a designer dress? I was wondering if I would be able to rent a designer gown for prom this year. I have a pretty large budget (not enough to buy that white Valentino at Bergdorf's haha) so that isn't really the issue. I'm just not sure where or who lends them out and for what kind of fees? Anyone know of a store or a website or anything? Thank you!

Fashion design question?? Im trying to find a modern day designer (EG: Versace, Cavalli, Armani, Valentino etc) who has designed a silk evening gown (Or just dress) similar to Jean Patou's 'Cape and Dress'. Can anyone name a designer whos designed a dress similiar to this?