The rednet API provides a simple computer networking model over RedPower bundled cables.

Functions for specifiying sides to be used for networking:
rednet.open( side )
rednet.close( side )

Functions for sending messages to other computers:
rednet.announce()
rednet.send( receiverID, message ) -- Send to a specific computer
rednet.broadcast( message ) -- Send to all computers

Functions for receiving messages:
rednet.receive( timeout ) -- Returns: senderID, message
You can also handle the "rednet_message" event to receive messages without calling receive(), the arguments are the same as the receive() return values.