The video resolution cannot be changed in-game. This game defaults to 640x480 on install. However, a person going by 'the bigg' have created a 'widescreen mod' (v2) that allows changing the game to any resolution.
Download --> http://www.gibberlings3.net/widescreen/
Instructions --> http://www.gibberlings3.net/widescreen/readme-widescreen.html
Basically, when you need to change resolution, you run 'setup-widescreen.exe' in the game install folder. It will ask you a series of questions. Enter in the width and height you want and off it goes. The program patches a ton of files. It may take some time to complete. When it's done, you now can run the game in that resolution.
A side effect of this is that every screen, other than the main ingame, are docked to the upper left corner of the screen and not resized like the main game screen. So, it may be hard to view text and so forth in these window when run at a high resolution like 2560x1600.
The good news is the main play screen fills the screen. In the same post from cranky above, user 'august' posted a link to a '1280x800' UI mod ('GhostDog's Planescape Torment UI' v1.0) that centers and expands the map, inventory, and other windows. I have not tried this mod yet mainly because it's restricted to only three resolutions (1280x800, 1280x768, and 1280x1024). I'll post updates if I do.
If you want to play in a window instead of full screen, do the following:
1. Open the file 'Torment.ini' in a text editor from the game directory:
"..\Planescape Torment"
2. Look for 'Program Options' group and change the following value:
Full Screen=1
from '1' to '0.'
When you do you get a warning window each time you launch the game
I noticed after using the 'widescreen mod,' the game now crashes when you load a save game in window mode
The same file also lists the following values under 'Movies' section:
BISLOGO=1
TSRLOGO=1
OPENING=1
I tried changing them all to '0,' but the intro movies still play.
The 'fog of war' is blocky at the edge (which you can see from the ingame screen shots in the next section). That annoys me. You can fix this by changing the following values in the ini file or from inside the game:
SoftSrcKeyBltFast=1
SoftBltFast=1
SoftSrcKeyBlt=1
SoftBlt=1
SoftMirrorBlt=1
What this does is make things rendered using software instead of hardware. Since my modern computer can handle the stress, it doesn't impact the frame rate at all.
Also, I find it runs smoother if I adjust the following:
Path Search Nodes=32000
Maximum Frame Rate=40
Thanks to 'Jason':
http://www.bootstrike.com/Torment/Online/tti2.html
Ok, I finally tried out 'GhostDog's Planescape Torment UI.' It's done the same way as 'widescreen mod,' except you run 'Setup-GhostDog's-PST-UI.exe' instead. Be sure to change to one of the supported resolution using the 'widescreen mod' first before you run the UI mod.
After it asks if you want to display the readme file, it'll prompt for the font type like so:
Install Component [GhostDog's Planescape: Torment UI]?
[N]o, [Q]uit or choose one:
1] PST UI with default fonts
2] PST UI with 30% bigger fonts
3] PST UI with 50% bigger fonts
I tried 1 first (size only changed for dialog not UI elements). Then it'll continue:
Installing [PST UI with default fonts]
Checking if Bigg's Widescreen Mod is installed with an appropriate resolution
Copying and patching 1 file ...
Found a 1280x800 installation of Bigg's Widescreen Mod
Installing the 1280x800 User Interface...
Once it's done, you're ready to go.
I've updated the screen change section with shots of all three AR from 'GhostDog's Planescape Torment UI.' Please note that the ones with the UI mod has a softer 'fog-of-war' effect because I changed it to software rendering as mentioned earlier in this section.
I've also noticed the game crashing on exit every now and then. I'm not sure if it's caused by the WS mod or the UI mod. Since they both patch a bunch of files.
I decided to try the three mods. You can find them all here: http://www.shsforums.net/index.php?autocom=downloads&showcat=14
I installed them in the following order:
1. PS:T Ultimate WeiDU Fixpack v3.01 (this mainly fixes bugs)
Install [Dialogue Spelling/Grammar Corrections (English Only)]?
[I]nstall, or [N]ot Install or [Q]uit?
Install [Subtitled Cutscenes]?
[I]nstall, or [N]ot Install or [Q]uit?
2. PST Unfinished Business v3.00 (restores game content)
Install All Recommended PS:T Unfinished Business Components?
[I]nstall, or [N]ot Install or [Q]uit?
Install Expanded Deionarra's Truth Mod?
[I]nstall, or [N]ot Install or [Q]uit?
Install Restored Cheat Items (Not Recommended)?
[I]nstall, or [N]ot Install or [Q]uit?
3. Qwinn's PST Tweak Pack v3.50 (lots of tweaks)
Install Banter Accelerator? If so, Choose interval between banters.]?
[N]o, [Q]uit or choose one:
1] Interparty Banter Every 4 game hours (20 minutes)
2] Interparty Banter Every 6 game hours (30 minutes) <Recommended>
3] Interparty Banter Every 10 game hours (50 minutes)
4] Interparty Banter Every 15 game hours (75 minutes)
5] Interparty Banter Every 20 game hours (100 minutes)
Install Maximized HP Per Level for TNO and Party?
[I]nstall, or [N]ot Install or [Q]uit?
Install Maximized Friends Spell?
[I]nstall, or [N]ot Install or [Q]uit?
Install Stackable Rings, Charms, Bracelets, Scrolls?
[I]nstall, or [N]ot Install or [Q]uit?
Install Scale of Souls?
[I]nstall, or [N]ot Install or [Q]uit?
Install Save Nordom! Tweak?
[I]nstall, or [N]ot Install or [Q]uit?
Install Tome Of Cheats (Not Recommended)?
[I]nstall, or [N]ot Install or [Q]uit?
Install Power Action Leprechaun Annah, by Black Isle?
[I]nstall, or [N]ot Install or [Q]uit?
Install Easter Egg Morte, by Black Isle?
[I]nstall, or [N]ot Install or [Q]uit?
Install Explore City Areas?
[I]nstall, or [N]ot Install or [Q]uit?
Install Rest Anywhere (Not Recommended)?
[I]nstall, or [N]ot Install or [Q]uit?
Install Identify All Items?
[I]nstall, or [N]ot Install or [Q]uit?
Install Use Floating Text Font Globally?
[I]nstall, or [N]ot Install or [Q]uit?
Install No Battle Music?
[I]nstall, or [N]ot Install or [Q]uit?
Install Early Glabrezus Tweak?
[I]nstall, or [N]ot Install or [Q]uit?
I haven't noticed anything different except for Morte is now a floating egg instead of a skull. But I haven't played that much yet.