Hey Stefano,
I really need to update that tutorial. It has a ton of details and some sample materials, but there is much room for improvement on it.
If you have any questions on it, you could ask in this thread and I and others will try to help out as much as possible.
FreeFlightDesign.com and FSdeveloper.com are 2 great website forums to get help from also by way of Gmax and FSX.
Bill