scientt: No worries. One suggestion would be to make a duplicate installation of your game and then modify resolution of widescreen mod. Try something smaller and see if it still causes crash. The newer versions of WS mod should give you option to fix saved games when changing res now. Still good to do any kind of testing like this with duplicate install in case something else breaks. Btw, what res did you use for XP VM?
So, I think it's now FIXED! Hurray!
I did as you suggested (I am listing all the steps):
1. replicated the installation directory to a new path at "H:\Games\Planescape Torment"
1b. I removed the files from the "cache" and "temp" folders
1c. I edited the torment.ini to match the new path
1d. I renamed the folder of the original installation to prevent programs (and me) from using links and shortcuts to that one.
2. I ran the widescreen mod to change the resolution. I set (lowered) the new resolution to x=1280 y=800.
2b. I said Yes when asked to update the save files
2c. I DID NOT enable the support for multiple resolutions this time (I think I did originally)
2d. I let it ran the whole patching workflow. Btw, I find it extremely neat that it actually handled that for me, well done! :)
3a. I changed the PlaneScape Torment desktop shortcut and the start menu shortcuts to point to the new directory as target and execute from there (two fields in the shortcut properties).
3b. Ran the game, loaded up a save game that crashed in the gallery and had no crashes. A part of the gallery was now shadowed (as unexplored) but other than that (which is not even an annoyance) no crashes!
+ I repeated the same process and set the resolution to 1440x900. Again, no crashes.
+ Again the same for 1600x900. And again no crashes.
What first occured to me was that initially (when I first installed the game) the resolution I had tried was x=1920 y=1200. But the game crashed immediately with some error because my monitor (23'' Dell UltraSharp U2311H) is 16:9 and did not natively support that resolution.
So then I looked up the "Monitor resolution" options for Win7 x64 (by right clicking on the Desktop) and picked a supported resolution from there. Hence, for Win7 x64 I tried 1920x1080 and 1600x900. For WinXP @VmWare I tried 1280x720 (if I remember right).
However, I just thought that none of these resolutions are actually listed in the guide in the list of "common resolutions". So this time, I picked one from the list that is also supported by my monitor and voila! Problem solved. Oddly enough though it now works with the 1600x900, so maybe it is the new path that fixed the issue? Or the fact that this time I did not enable support for multiple monitors? I don't know for sure.
I have not tried this in the Windows XP SP3 installation (yet).
Note: I do have the ddraw fix on top of the mods and patches suggested in the guide (PST-Drawfix: v2.1.1)