So after several attempts at a solution, Torment still crashes. If the widescreen mod is causing this—I do believe it is—, then playing the game without it should work. The only thing is starting over now would kind of suck; can I use my wide-screen mod save file with a game that doesn't have the widescreen mod?

This doesn't work?

http://www.gog.com/en/forum/planescape_torment/yvana_art_gallery_crashes/post90

I think I performed that patch manually as per another thread on the same topic. It modifies a couple of x / y resolution values on three or four lines in the Torment executable file, right? If that's true, then it didn't work, no.

Edit: tried the patch anyway to no avail. The game still crashes after a couple of outdoor -> indoor transitions.