Here is a quick HowTo on programming your own keyless entry:

1) Turn ignition to OFF.
2) Locate the Data Link Connector, its a black 16 pin connecter that is under the driver's side dash, right where your right knee would be. You have to look up into the dash from below to see it.
3) Ground pin 1 of the Data Link Connector by taking a wire or paper clip and running it from pin 1 to pin 4. Pin 4 is ground so you can just short pin 1 to 4 and it will be grounded. Grounding pin 1 tells the system you are ready to reprogram it.
4) Close all of your doors.
5) Turn the key to ACC then back off. The power door locks will lock/unlock. This is the signal that the system is ready for reprogramming.
6) Push a button on your key fob, doesn't matter which button.
7) If you have 2 key fobs, then press a button on the 2nd fob within 1 minute of pressing a button on the 1st fob. Both must be programmed at the same time. If you only have 1 fob then press a button 2 more times to signal that you only have one.
8) The doors will lock/unlock to signal the codes were received.
9) Remove the jumper wire from the data connector.