Hey Willy,
Great to have you over here! The airport files, textures etc are not the same in FSX as those in FS9 for any airport as far as I know. You can however, with various results, port over some airport scenery to FSX (see below though before you do). For making up AI, the airport ICAO codes stay the same.
I pretty much just moved all my FS9 AI building tools over here and it all works pretty much the same way. Lee Swordy's TTool is essential - you will get an error message when trying to open it but disregard as it compiles Traffic.bgl's from the three text files the same way. Also, to make "AFCADS" (they're not called that anymore) you need Airport Design Editor. With that you can create or modify airport files, add parking, library objects, etc.
One word of caution - if you mix any FS9 Traffic files with FSX they will kill your AI and make it disappear. There are some conversion utilities around that simply convert FS9 > FSX Traffic files, including Airport Flight Planner. All freeware.
Been on an AI building binge out in the Solomon Islands the past few days.
expat