I am installing everything from scratch, and want to make sure nothing is incompatible. So which do I install first? The Orbx North American scenery, deactivate it, THEN install Ultimate Terrain and then Ground Environment? Thanks

Install in any order I believe. Just ensure that all the Orbx files are both the UTX and GEX and you should be fine! Though, go look over at the orbx forums - thats the best place to ask :)

Just as Aidan said... "Orbx files are both above the UTX"... I doubt there is a preferred order but make sure you have all the updates ready to go and follow the instructions regarding patching/upgrading. A good place to look is NickN's excellent post regarding FSX Setup and Tuning .