Are you sure you read the tutorials properly? The easiest way to do this is to setup the camera in the room you want it in. Make it follow a func_train for the side to side movement. Then, put a trigger in the room you want to 'view' it. Make it a brush shaped like a screen or something. This is what will happen:
1.) Player 'uses' the screen
2.) This triggers the camera which is in the other room
3.) The camera endlessly follows the func_train creating the side to side movement
You'll have to figure out how to unuse it because I can't think at the moment.