I really want to enjoy the game, but I have a pretty big problem.

I use the DPfix so that I can play on 1280x1024 (so that the entire picture can fit on my screen), but since then, the game started crashing often. It always seems to be at complete random.

I'm mostly replaying Chapter 1 Episode 2 to get all the sidequests. I got a few, but the game decides to crash always when I'm almost done with the day. At first, I thought it was because I skipped the cutscene. But when I retried, it crashed seemingly at a random point (and at one point, on a loading screen).

This game is really driving me crazy. I want to love it and play more, but I wish it would stop crashing. And I wonder if there was any way to aleviate that (I tried changing the compatibility to Windows 98 and run the program as Administrator, but it didn't work).

Thanks in advance.

Try re-installing PhysX.

I wonder if I need a specific version since I use an AMD card (and I think PhysX is an nvidia software).

And should I uninstall the version installed first?

OK. I did re-install it and I managed to replay the chapter and complete two of the quests. When I replayed it again to finish the other ones (to get the guitar), the game crashed again (Runtime Error). Guess I have to reboot my computer each time I replay a chapter.

You do need to uninstall the version of PhysX that is installed, reboot then reinstall. Anyway, rebooting is a good idea and doing that combined with running as admin and windows 98 compatibility. Did you check the DPFix settings file as well to make sure it is set how you want it?