how to program a new key

I want to get a second key for my 02 Venture and they tell me that I cannot get one cut that I have to buy a special key and program it the garage wants 34.00 for the key and 34.00 to program it anyone know how to program the keys?

Here is a link on the PK3 Key Programming:
http://www.my-chevy-venture.com/passkey-III-pk3-programming.html

Thanks,
Donnie Lee