I don't think it's a dress underneath... it's similar to a petticoat/long-tutu. You can buy a waist petticoat like this one (
http://compare.ebay.com/like/2205693...Types&var=sbar ) I've worn such things under dresses for that flared out look.
Is there a link for the contrail mp3? I've seen the PV but I wanna listen on my iPod ;_;