Hi ya

I travelled from London to Orlando with my ''monstrous meringue'' lol lol back in 2007. There was no way I was going to put my dress in the hold and a good friend of my told me about the empty box company.
http://www.emptybox.co.uk/products_travel.aspThey sell specialised travel boxes for wedding dresses in really beautiful designs. I actually have kept mine in the same box since we got back. They are to the exact maxiumum measurements allowed on board.
I agonised over this for months before the wedding but on the actual day it went like a dream. As others have mentioned it will class as your 1 piece of hand luggage. This was no a problem for me as my Hubby never takes any so my handbag was theoretically his that day LOL. The box was really heavy but I would not let anyone else carry it (yes I was one of THOSE brides [:X]).
Once on board cabin crew were fantastic and immediately took the box away (I believe to the little waredrobe) to stow for me. They even let me check on it during the flight [ii]. Once we landed they brought it right over and of course it was safe and sound. All in all Virgin were fantastic about it.
If I can help any more please let me know [:D]
Oh and CONGRATS on your up and coming wedding [y]