Keyless entry system

I have a 2002 Pontiac Grand AM, I'm looking into adding a Keyless entry system. I'm wanting a OEM style system from GM. Doesn't anybody know where i could purchase a kit. I found one, Link (http://www.oemradios.com/parvke1gmkey.html) , but is any where that I could read about it. Also, has anybody ever installed one? Did you run into any problems? Please Help!!
Thanks

cant be that hard