If I run the game in Fullscreen mode, it has a lot of tearing. I've activated vsync from Catalyst but it doesn't work. How can I solve it?

Unfortunately, I don't know how to help you... have you tried asking GOG support, or taking a look at the game's support page? If all these fail, my best bet would be going directly to the AGS technical forums, since people in here are not particularly active -- I speak from personal experience; Primordia GOG forums aside, all my questions remain unanswered, some have been posted a week ago. It seems people are more interested in complaining about the games they bought than actually helping us fix the issues we're having with them.