On the 2005 and later systems, the team number has to be set greater than 2048 in order to enable alternate channels. In your case, it might be most convenient just to flip the leftmost switch on the OI and use team number 3045 for the other (older?) robot. You will have to use the tether cable in order to get the number transferred to the robot.
Once you have the team number changed, use the channel select switches to choose the other channel. Here's the key:
Code:
1 2 3 4 Channel
X ON ON ON 04
X ON ON OFF 13
X ON OFF ON 22
X ON OFF OFF 31
X OFF ON ON 40
X OFF ON OFF 01
X OFF OFF ON 40
X OFF OFF OFF 40
A couple of weeks ago, we had no fewer than four of our robots running around simultaneously, all on separate channels.