The procedure should be similar for all GM cars with the 3800 Series
II 3.8L V6 engine including the Buick Regal, Chevy Impala, Monte
Carlo, and Bonneville.
Here's the guide - http://www.paulstravelpictures.com/GM-Pontiac-Grand-Prix-Engine-Coolant-Antifreeze-Change-Guide/
I hope someone finds it to be useful.
Cheers,
Paul