Creating a realistic scenery

Hi everyone,

I'm new to TerraGear. I'm using FlightGear and I've seen the realistic scenery that could be used. Due to the fact that I'm using FlightGear as a base for my thesis and the realistic scenery is good new, I'm asking how I can create one for my country, Italy. The main question is how I can add the textures to the scenery created by TerraGear. I've looked into the directory of FlightGear that holds the data about scenery but I don't understood how I could change the textures used by the program. 
The question is very important because I use FlightGeat as a 3D virtual trainer for the pilots but it's impossible if the scenery isn't enough realisic.

Hi,
Luca

PS: I've also tried to use the one created for San Jose, but I'm not able to corretly load it. I've used the two packed files "KSJC-Photo-1.0.tar.gz" and "KSJC-Photo-2.0.tar.gz" that I've found in an ftp site.