Yes, the problem I had was that I didn't get a manual with mine. I have since got one and the procedure for mine (a 2004) is:
1. turn ignition to 'ON'
2. press and hold 'UNLOCK' on a GOOD PROGRAMMED fob for at least 4 but not more than 10 seconds.
3. press and release both the 'LOCK' and the 'UNLOCK' buttons on the fob you want to program simultanously.
4. press and release any other button on the fob you want to program. A chime should sound in the Liberty confirming the programming.
5. This is important - it doesn't really spell this out in the owners manual but at this point your previously unprogrammed fob works - but - your previously programmed one WON'T! You now have to press both the 'LOCK' and 'UNLOCK' buttons on the previously programmed one and then press and release any other button and again you should hear the chime and then you will have two programmed fobs. They may not immediately work, you may have to turn the ignition off and then on again, I did.