According to the 2003 Owners Manual:
You can program new keys to the system if you have two valid sentry keys by doing the following:
1. Cut the additional Sentry Key Transponder blank to match the ignition switch lock cylinder key code.
2. Insert the first valid key into the ignition switch and turn the
ignition switch ON for at least 3 seconds but no longer than 15 seconds.
Turn the ignition switch OFF and remove the first key.
3. Insert the second valid key and turn the ignition switch ON within 15
seconds. After ten seconds a chime will sound and the Theft Alarm Light
will begin to flash. Turn the ignition switch OFF and remove the second
4. Insert a blank Sentry Key into the ignition switch and turn the
ignition switch ON within 60 seconds. After 10 seconds a single chime
with sound. The Theft Alarm Light will stop flashing, turn on for 3
seconds; then turn off.
The new Sentry Key has been programmed. Repeat this process to program up to a total of 8 keys."
Without 2 valid keys, it is back to the dealer for them to reprogram.
Also, could check the Chrysler PT Cruiser Sedan - Convertible Owners Manual