Text in case link ever moves or otherwise breaks:
1) Enter your car with your ignition key, open the driver's door, close all of the other doors and make sure the driver's door is unlocked.
2) Insert and remove your key from the ignition twice, close and open the driver's door twice, insert and remove the key from the ignition once and close and open the driver's door two more times.
3) Insert your key into the ignition again, leave it there, close the driver's door, cycle the key "On" and then back "Off," and remove the key from the ignition.
4) Wait for the door locks to cycle and press and hold the "Lock" and "Unlock" buttons on your remote for two seconds
5) Release the two buttons and press and hold the "Lock" button by itself for two seconds and wait for the locks to cycle. This will complete the programming sequence and you can remove your key from the ignition.
But I used a different procedure I found. It was more simple.
1. Hop in car, close door.
2. Turn key On/Off eight times quickly, leaving in On position. The computer will respond with lock/unlock door for program verification.
3. Press any key on each of the fobs you want to synch. Computer will respond with door lock/unlock for verification with each fob.
I neglected to mention this was for an 01 Sable, if this matters.