A friend just got me this game and I tested it and it works fine, except that when I quit to the desktop, it says that the game has stopped working. The rest of the game and the saves work fine, but this issue just kinda bugs me. Can it be a problem and how can I fix it?

This was fixed in latest version of unofficial patch.

If you don't want to use an unofficial patch as scientt said (I didn't know about or I would have used it) you could also follow the instructions here:
http://www.gog.com/en/forum/planescape_torment/windows_7_64bit_fix_for_crash_on_exit_screen_shaking_flickering/post8
and here:
http://www.gog.com/en/forum/planescape_torment/windows_7_64bit_fix_for_crash_on_exit_screen_shaking_flickering/post9

The "emulate heap" was the only adjustment I needed to stop the crash on exit. Are you referring to the Torment Ultimate WeiDU Fixpack?
Or should I be looking for something else?
I don't want any mods but bug fixes are ok especially the crash on exit fix.

Thanks.

OOPS! Nevermind I found it referenced:
VERSION 4.13: Includes some new engine fixes, the highlights being fix to "Ice Knife" spell and getting rid of the annoying crash on exit for Vista and Win7. Also, the addition of French translation.

Thanks anyway!

Oopsie! I got to this a little late. Oh well... I'll keep this in mind in case the issues goves me more trouble. But thanks for the help!