Robert Blake wrote:
When playing cards from your hand, is it possible to put an Attachment or an Ally card in the other player's area? Do we have that choice?
Yes and No.
From page 25 of the rules
Control and Ownership
When a player plays an ally card, it comes into play under his control and is placed in his play area. If another player takes control of that ally, it is moved to the controlling player's play area. Ally cards cannot be played under the control of another player, they can only change control through card effects.
When a player plays an attachment card, he has the option of giving control of that card to another player by attaching the card to one of that player’s characters. Players always assume control of attachments that have been played on their characters. If control of that character changes, so does the control of any attachments on that character.