So, this is not a new topic but I figured it would be helpful for some to see a recent post about this. I felt like playing through the game again and had to go through all this mess :)

Out of the box the game has some issues with damage calculations due to the game running at higher framerates than originally expected. For example, you may notice that shooting at enemies produces the damage hit sounds but doesn't actually result in visible damage. In addition, the PBCs overheat in normal mode after just a couple of shots - this is not how it should be.

The usual advice is to limit your framerate using 'adaptive refresh rate' or similar settings in your video card config.

What worked for me was using the latest version of dgVoodoo2, since it allows limiting the framerate to a specific number. Setting it to 30 eliminated any damage issues for me, PBCs only overheat in rapid fire mode, and no crashing between missions :)

Setup:
- Download dgVoodoo2: http://dege.freeweb.hu/dgVoodoo2/bin/dgVoodoo2_76_1.zip
- copy these files into your I-War root directory (C:\Program Files (x86)\GOG Galaxy\Games\Independence War Deluxe\):
-- dgVoodooCpl.exe
-- dgVoodoo.conf
-- 3Dfx/x86/Glide.dll
-- 3Dfx/x86/Glide2x.dll
-- 3Dfx/x86/Glide3x.dll
(don't copy the 3dfx/x86/ subdirectory, just the files)

Next, you'll have to edit the .conf file. dgVoodooCpl.exe does not expose the frame limiter setting.

For the config file, this is what I'm using: https://pastebin.com/jDfEKG4v

The noteworthy settings are:

[General]
OutputAPI = bestavailable
Adapters = all
FullScreenOutput = default
FullScreenMode = true
ScalingMode = centered
ProgressiveScanlineOrder = false
EnumerateRefreshRates = false

Brightness = 100
Color = 100
Contrast = 100
InheritColorProfileInFullScreenMode = true

KeepWindowAspectRatio = false
CaptureMouse = true
CenterAppWindow = true

[GeneralExt]
DesktopResolution = 1920x1080@60
DesktopBitDepth = 32
DeframerSize = 1
ImageScaleFactor = 1
CursorScaleFactor = 0
DisplayROI =
Resampling = bilinear
FreeMouse = false
WindowedAttributes =
FullscreenAttributes =
FPSLimit = 30
Environment =
EnableGDIHooking = false

[Glide]
VideoCard = voodoo_2
OnboardRAM = 8
MemorySizeOfTMU = 4096
NumberOfTMUs = 2
TMUFiltering = appdriven
DisableMipmapping = false
Resolution = 1440x1080@60
Antialiasing = 4x

EnableGlideGammaRamp = true
ForceVerticalSync = true
ForceEmulatingTruePCIAccess = false
16BitDepthBuffer = false
3DfxWatermark = false
3DfxSplashScreen = false
PointcastPalette = false
EnableInactiveAppState = false

I set the game resolution to 1440x1080 since I'm using a 1080p display and wanted to keep the 4:3 aspect.
YMMV, but these were the magical combination of settings for me. I didn't have the desired results using the borderless fullscreen/windowed mode, possibly due to the frequent resolution switching between the game/cutscenes.

Launch the game through iwar_start.exe as usual.

If you are wondering if it's using the right wrapper, change 3DfxWatermark = true, and you should see a small 3dfx logo in the lower right corner.

Bro! For YEARS, I've been on and off trying to get this game to work correctly. THIS worked for me! I love you! Thank you! Tried dgVoodoo2 over and over, but the settings never seemed to make a difference. Again, this did. Much appreciated.

it works! just installing the dgVoodoo and editing it's config to your setup worked! I can finish this game again, this winter

Oh My God it works! i set my resolution to fill my whole big screen tv and it looks so wonderfull. im so happy :-D

dgVoodoo2 doesn't work for me. I did everything correctly, I have been using dgVoodoo2 for a long time, but for this game the watermark doesn't show and my settings have no effect, the game always play on its original resolution in little box on the center of the screen. I also tried setting the resolution to 1080p in the nGlide configurator but nothing changes.

Problem solved.
The reason is the game was never even trying to use 3DFX. Had to shortcut directly to IWar.exe and add command line argument " -b -16" which forces the game to run in 3DFX mode.
The problem seems to be the launcher only works when Windows 98 compatibility mode is enabled, sure the game runs but no 3DFX, so no Glide, no 3D acceleration. When I turned off the Windows 98 compatibility mode, the launcher i.e. iwar_start.exe wouldn't work and throws an error. Somehow Defiance doesn't have this problem. So no launcher no big deal, all you lose is the intro video which can be played separately anyway.