Looks like it might be a bit more expensive and labor intensive to get remote start.
I went to Crimestoppers website and downloaded the installation instructions, seems we'll need a data interface module for 03-05 on the Class II databus, and 06 on the CAN bus. Looks like that interface is needed to talk to all the vehicle computers to monitor the engine crank and to tell the BCM to unlock the doors when you have the aftermarket remote start installed, since the BCM won't want to unlock the doors with the ignition on without a key in it.
That's just a quick first look. I am curious though, I have remote start on my STS and I love it in both summer and winter. Now I need to see the options for my Escalade and Audi since those will see more winter driving than the STS will,