Is there a simple ethernet splitter?

[Josef Lowder]

.
On my 2-Wire modem/router, there is a single ethernet 
port that I have my main computer plugged into, and I 
have two other computers in our home that connect via 
wireless cards.  Now, I've just added another computer 
that I'd like to connect via the ethernet port, if 
possible. 

Is there such a thing as a simple "splitter" that would 
allow me to plug in two computers into a single ethernet 
port on my 2-Wire modem/router?