One thing is missing: the registry key to modify from the "Device Setting" registry folder is ResolutionIndex

But I can confirm that that registry trick for widescreen works, tried just now and it's perfect.
Values for the resolutions are not right, anyway.

I presume that it's related to directX and "enumeration" of video modes

For instance to have a 1920x1080 resolution on my PC I had to use decimal 39 (hex 0x27), so I think the values may differ from configuration to configuration.

Does anyone know if there is a tool/program that gives a list of all resolutions supported by the videocard in DirectX (modes) and the "code" for each mode (that number to put in the registry to make it work at that specific resolution ) ?

You don't have to look for any folder, you have to change the value through the registry editor of windows..

Here's a detailed explanation on how to procede:

1) Click Windows START BUTTON and in the search box type "regedit.exe" (without quotes) : when it finds the program click on its name (regedit.exe) to launch it;

[ or, in alternative, press the combination of keys : WINDOWS+R (WINDOWS = the windows key on the keyboard, usually placed between the CONTROL and ALT keys) and then type "regedit.exe" (without quotes) in the search box]

NOTE: the registry editor will ask for higher privileges at launch through UAC on launch, confirm that request with YES. If you have an user account with very limited privileges you may be not able to run the registry editor and so you can't modify the parameter to change the resolution.

2) If you follow step 1 correctly ..then you should be in the registry editor of windows. There's a hierarchical tree of registry entities in the left-hand panel ..

You'll have to star your search from the root (Computer) and follow the entire path of the registry key provided, which is (for the 64bit edition of windows only) : HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Pivotal Games\Conflict Desert Storm\Device Settings

Every slash indicates a new sub-level in the registry hierarchy..
So.. here's the steps you have to follow:

a) COMPUTER: click on the black "arrow" near the root item (computer) to open its sub-items..
There should be five HKEY_ items.

b) HKEY_LOCAL_MACHINE: click on the black "arrow" near HKEY_LOCAL_MACHINE to open sub-trees, then find the registry item "SOFTWARE"

c) SOFTWARE: click on the black "arrow" near SOFTWARE and look for the sub-item "Wow6432Node".

d) Wow6432Node: click on the black "arrow" near this item and look for the sub-item "Pivotal Games"

e)"Pivotal Games": click on the black arrow and look for the sub-item "Conflict Desert Storm"

d)"Conflict Desert Storm": click on the black arrow and look for the sub-item "Device Settings" : you're done, click on it (Device Settings) to open in the right-hand panel the associated registry keys.

3) There are a dozen of registry keys inside the "Device Settings" registry folder: the one you're looking for is "ResolutionIndex". Double click on it to open a windows where you can try some other values.

I attach a picture to clarify the entire procedure; it's very easy, in fact .. but if it's the first time you tamper with the registry editor may be a bit confusing

Anyway, as I wrote in my previous post... the values on that list weren't right for me (I had to use decimal 39, hex 0x27 to have a 1920x1080 resolution, instead of decimal 37)