Personally I find castling with my own rook rather unimaginative -- castling with the opponent's rook gains material and nestles the king away safely while pieces are still being developed.
how exactly do you castle with the opponent's rook?
The same way you castle three times in the same game.
you can castle one time, then move your king all over the board "castling" but how can you, for example, make your king on e1 castle with the opponent's rook on h8?
@Screener: Never move the same piece twice until you have finished developing all of your pieces without good reason.
@bobyyyy and AcivilizedGentleman: Thanks for the advice and illustration, respectively.