If you are using Cubase SX/SL, you can use Cubase's System Link in conjunction with Vstack; I don't think VST 5.1 has System Link. It is a rather complicated setup though, but I think I can help you somewhat if you go that route. A far better option, IMO, is FXTeleport, especially if both pc's support gigabit lan.
You can also treat the remote pc as a sound module with plain midi connections. You should be able to slave the remote pc to the main pc using s/pdif connections.