The point of the union room is to talk and trade with a group of friends with the wireless adaptor.
in the union building
http://www.neoseeker.com/Games/action_replay/
Just go to a union room in both games and offer to trade
the union room
upstairs in the Pokemon center first door
go to the union room with a friend
make your Pokemon hold pokeballs then trade them over
Go to the Union Room.
To change your appearance in Pokemon Platinum's Union Room you need to talk to an NPC in the Oreburgh Pokemon Center. The NPC in question has the appearance of a Psychic trainer.
If you have two DS's, or a friend with a DS, you can trade between the two games by going to any Poke Center and going into the Union Room. You can trade between the two games.
of course u can
The Union room in every pokecentre.