On the Hand Editor, after creating the hand press the "play" button and then choose the seat you want to be the dealer (click on the seat for ex. click on North). A square with the letter D will apear in the position of the dealer. If you want to change it press another position. Click on this square to change vulnerability. I read somewhere in the forum, that if you use your saved deals for a turnament or some other functions of the site (not a teaching table) bbo will choose the dealer and vulnerability automaticaly by the default order that is used by its program.