Programming a New key

Anyone here work for Chevy, is a locksmith, or has programed a key before? A locksmith once programed a key but to the point where it could start the car but wont stay on. He had a little trouble with it and I'm not convinced he knew what he was doing. It got to the point he didn't even charge me for the key. I have the key and would like to do it right.

Ok, I found it and thought I'd post it for anyone who needs it.

1) Insert the "Original" (working) Key.
2) Turn the Ignition to ON (RUN), but do NOT start the engine. Turn the Ignition OFF and remove the key.
3) Within 15 seconds insert the new "duplicate" key and turn the Ignition to the ON position. The Security indicator should light for about 2 seconds to indicate that the new key has been programmed.
4) The new key should now be able to start and run the van.

I am glad to see that this concern has been resolved. Please feel free to contact me directly if you have any questions or concerns in the future. Thank you.

Tricia, GM Customer Service.

Update: Tricia has been kind enough to check into this for me but apparently the PK 3 key reverts back to only starting the car then shutting off. after using the above programming method. I'll post any resolutions to this issue incase it happens to anyone else.