Putz, Welcome to Just Commodores.
OK, the question has been asked, and you can always use the search feature to look before you post.
But in answer to your question how easy it is? It's not easy enough to be worth doing.
The wiring and plumbing is similiar in terms of power and ground... that is where it ends. The dial controls are mechanical with cables and air hoses. the climate control variety is just that electroically controlled. And while it is not impossible to do, it will be a headache to attempt.
you'll need to take the bottom console off around the gear lever. remove the radio, source a climate control fascia, source a climate controller Mid to high level BCM, getting your keys reprogrammed to that BCM, engine coolant (climate control dependent sensors) cabin temp sensors. $200-500 depending on where you get it from. then you'll spend most of the day wiring it and working out how to make it work.
http://forums.justcommodores.com.au...02-2004/13282-climate-control-vy-acclaim.html