If you can separate the snakes it would be a good idea, but it is unlikely your other snake will become sick from the respiratory infection of another snake. Most respiratory infections are caused by opportunistic bacteria that are present in healthy snakes. The bacteria don't harm the snake until the snake's defenses are weakened due to poor husbandry or stress.
Here is a episode of reptile radio where Dr. Scott Stahl talks about this and some other stuff, it's pretty sweet.
http://www.blogtalkradio.com/reptile...ile-Veterinary