Home Network :: How Best To Share A CAT5 Connection

I have a Linksys/Cisco wireless router. For the purposes of a high def throughput, I have a wired connection from the router to a Windows Media Center appliance in a separate room.However, now I have a second media appliance (Roku device) that I want to run in a wired fashion as well. Here is the thing, I don't want to run a second Ethernet line from the router to new roku device. Is there some way I can share the existing ethernet line between the roku device and the media center appliance? Ideally, since the two devices would never be used at the same time, I was hoping some other network device (another router?) could be hooked up to split the line between the devices. Worst case, is there some simple splitter I can use? Obviously I am trying to avoid the worst case scenario: switching the ethernet connection manually between the two devices every time I want to go from one to the other.