Just started BG1 for the first time today and have had 3 crashes like this in starting town.
Running Win7/64, widescreen mod (v3.05) and fix-beregost patch. No GUI mod.

After the first crash I save before entering a building but was wondering if anybody ever got to the bottom of this?

I haven't played the game in a while, but as far as I remember I was never able to fix it.

However accesspanels fix above looks to be worth a short

Hmm, I never had any previous saved games.

I haven't done any alt-tabbing and I'm still getting the CTD in the starting town. It just happened to me when I was fighting the rats. I do have the widescreen mod installed as well, but no other mods. Running Windows 8.

I imagine there isn't much GOG can do, but it's a bummer to think I may have to save my game every 5 minutes.

Mm.. i am in the end stage of the game and now i can't enter any building with out the game crashing. so sad. i do will try to uninstall the mod, but it worked fantastic so far just not now.
I fear i can not finish this game.

the uninstall an reinstall of the game without any mod works. now i can finish this games. yeah :)

of interest:
http://www.gog.com/forum/planescape_torment/crash_with_widescreen_mod_possible_solution/post8

( make sure you backup your save'd games before switching between different version of the widescreen mod )

True. In my case the saves were damaged. The good was that i had a backup. But i noticed that the mod also crashes the game sometimes.