IÂ'm not really into sci fi stuff, but itÂ's possible. You can do it with normal triggers.
When a person or vehicle enters the trigger area, the are setPos'ed to the desired location. This is how the gates work in the movies, right?
So, the model for the stargate just has to look cool, I suppose. It doesn't have to have much fancy scripts included in it. I would guess that you can borrow a lot of ideas from BAS Chinooks helicopters. Download the ME-47E, unPbo it and have a look inside. BAS used a cargo script that relied on setPos (I think). When a vehicle entered a certain area (inside the helicopter, to be exact) it was setPosed in the cargo space until you released it via the action menu.