If you do them individually you can select Leave a copy in current forum
and it should leave a copy in the forum it was in and you will see the thread moved to the new location-however replies from that point on are not duplicated in both threads. If you use the 'Bulk' move option in the forum itself then you won't have that option. Board Move is a whole different option-that involves moving threads from one board as in from support here to the sample board listed in the BbRing below-forum moving is what I think you're refering to Diana. If not then you must be an admin on both boards you want to move threads between or the Board Move will not allow it.