Ok, can someone please explain to me like I was 5 years old, how do I get Planescape to work? I am getting the classic "No valid video modes supported" BS, regardless if I have the Widescreen mod. I have the Widescreen mod and have followed the step by step and it still refuses to work.
Furthermore, I cannot get Ghostdogs UI mod to open. Whenever I click the UI icon after downloading, I am taken to a blank Internet Explorer window.... I sent a support email to GOG and have received no response. First game I have brought from here, and I am pretty disappointed to say the least.
Could somebody explain what I am doing wrong as dumbly as possible please :(

Okay, so finally got the Ghostdog mod to open. unzipped the file into the Planscape Torment GOG file... Now whwn I click the .exe I just get:

** ERROR ** [SETUP-GHOSTDOG'S-PST-UI.TP2] not found.
Make sure that you have unpacked the archive correctly and
that you are not trying to run this file from inside an archive.
ERROR: Unable to find DIALOG.TLK in:
dialog.tlk

Please run this program in your Infinity Engine game directory.

FATAL ERROR: Failure("Unable to find DIALOG.TLK")

Press ENTER to exit.

I have spent nearly all afternoon just trying to get this game to work. Why does GOG sell games that do not even work properly??

First of all, don't panic. The Infinity Engine games like PS:T can be tricky to run on modern systems, since they're old and some of the compatibility issues don't have a universal solution and can't be simply patched out. That said, most people do get them to work properly, so there's no need to worry yet.

You have not specified what your OS is, which is important because post-XP Windows versions are really picky about what the programs are allowed to do. For example, on Windows 7 older games should never be installed into the default Program Files folder, since they can't deal with restricted access without being given admin rights. Putting them into a neutral location, e.g. "C:\Games", prevents a lot of these errors from happening.

All mods expect to be unpacked directly into the game's main folder (right where Torment.exe is), not into a subfolder, so always make sure they're in the correct location before running them, or they won't be able to find the target files. They also expect to have full access to the folder, as noted above.

The Widescreen mod can fail to work at some resolutions, depending on your hardware, so, again, no universal fix. There are lots of threads dealing with these errors, both here and on other forums. Try other resolutions if you can't get it to work at the max one.

TL;DR (applies to most classic games sold here):

1. Posting your OS/hardware details right away will get you some help faster.

2. Install games into a folder that is not Program Files. Depending on your OS you may even wind up having to put them into the user folder as these should always have free access.

3. When installing mods, unpack them into the game's main installation folder.

(Also - welcome to GOG, and please do not judge its quality by one game category that is very well known for being a pain to make work properly. Plus, mods are third-party unofficial fixes, so GOG can't - for various reasons - be responsible for them. And support usually won't respond during weekends, they get to have some rest, too.)