Effect using the drawing api

http://www.dynamicfactory.com/003/ex_dyfacto_menu/v7b/first.htm

This kind of pulled down/up effect, as soon as it loads the gray background kinda pulls/folds down — this one also curves! — I like this effect (though over used on the web realy, I think) any ideas/tips/tutorials on achiving this effect ?

Can you see what I mean ? also appears on some of the content boxes in the site, like a small strip at the bottom of the images when you click on partnership, adaptation and security.

TIA