You were right about the special edition making it impossible for the retail edition to install. I uninstalled the special edition, but kept a copy of the folder elsewhere, so now I can still run it using its no-disc patch.
Then I installed the retail (Italian) edition normally and added the Compatibility Patch. I got in-game but the intro cutscene didn't play. So, I added the no-disc patch linked in this topic. The cutscene played but the game crashed after the loading screen (as I'd reported on my previous message).
I figured that the only way that works for me is to put in the GAMEDATA folder the files "tt1.cnt", "tt2.cnt", and "tt3.cnt" taken from my CD (not from the no-disc patch archive). Also I wasn't able to copy "tt4.cnt" from my CD, but I've read here that this is expected and that file shouldn't be required. Anyways, if I try to add tt4.cnt from the no-disc patch archive, the game starts crashing again. Maybe those cnt files are slightly different in each language release?

