==Method==
Hack
ini and hex adjustments
Step 1; Resolution:
Go to; My Documents\Deus Ex - Invisible War. Open user.ini and find the following (probably close to the bottom) to set your resolution;
FullscreenViewportY=xxx
FullscreenViewportX=xxxx
Step 2; HUD size:
Go to; ...\deus ex invisible war\System. Open default.ini and find the "FOV__d=" setting.
There's no "correct" setting as such, but for the purpose of screen shots I've used these values;
4:3;
FOV__d=67
16:10;
FOV__d=58
16:9;
FOV__d=53
Smaller values for wider aspect ratios.
Step 3; Field of View:
In the same folder (...\deus ex invisible war\System) open the Engine.d2u file with a hex editor. It would be wise to make a backup copy of this before editing anything. I know that's obvious, but safety first.
Search for the hex string "AA 42". Before I go any further, here's what that means (I think);
----------------------------------------
Hexadecimal value | AA | 24 |
----------------------------------------
Decimal value | 170 | 66 |
----------------------------------------
Engine value | fov 85 | float |
----------------------------------------
You should find three instances of this string that represent the following values (I think);
FOVAngle=85.000
DesiredFOV=85.000000
DefaultFOV=85.000000
The three "AA" values will be changed. The "42" part must be left alone.
For 16:10;
change "AA" to "CC"
giving you an FOV of 102
For 15:9;
change "AA" to "D4"
giving you an FOV of 106 (untested, but mathematically, has to be correct)
For 16:9;
change "AA" to "E3"
giving you an FOV of 113.5
I am aware that these aren't the orthodox numerical adjustments, but they are correct. Below is a picture which I'm hoping will be pretty self explanatory.

In the Unreal Engine 2 Runtime (which is what I used to figure this out) the FOV is set to 85 in the source code, but overridden to 90 in the User.ini. So if you want to use a derivative of the more standard FOV 90 setting, make one of these adjustments;
For 4:3;
change "AA" to "B4"
giving you an FOV of 90
For 16:10;
change "AA" to "D8"
giving you an FOV of 108
For 15:9;
change "AA" to "E1"
giving you an FOV of 112.5 (again untested, but...)
For 16:9;
change "AA" to "F0"
giving you an FOV of 120
And another three screen blend;

For these FOV settings I used the hex editor avalable here. It's freeware and doesn't require installation, so yay.
First unpack the xvi32.zip, open XVI32.exe and use it to open the Engine.d2u file in the ...\deus ex invisible war\System folder. Next use the Search-->Replace... function and you'll see this window;

That's how it would be filled in for an FOV of 108. Notice the "D8", that's where your new value goes. You'd put "B4" for an FOV of 90 and so on. Next just hit Replace all and you should see this;

Hit OK, save and you're done.
== Method to correct cut-scenes ==
The in-game, engine-rendered cutscenes were a bit tricky in that I couldn't get good screenshots. Sometimes things seemed fine and sometimes the tops of heads were cut off. I guess I'd go with vert- here, but it's nothing too disruptive.
The intro and ending cutscenes are prerendered bink files. They stretch.

1280:720 Plainly, that helipad is too elliptical to be correct.
If you're as anal about these sorts of things as I am, you'll want to fix that. So, download and install the RAD Video Tools. Open and navigate to ...\deus ex invisible war\content\DX2\VideoTextures.

The relevant files are;
EndgameIlluminati.bik
EndgameJC.bik
EndgameStranger.bik
EndgameTemplar.bik
Intro.bik
Single click to select and hit the Bink It! box in the lower left corner. You should see this window;

For the sake of simplicity leave everything other than the highlighted cropping section alone. Hit Bink to start encoding and expect it to take some time. The above setting would apply if you intend to use a 16:10 resolution. The "Endgame" videos are letterboxed to 16:10 so you'll need different settings for them when using wider aspect ratios.
For 15:9 use;

for Intro.bik and;

for the Endgame videos.
For 16:9 use;

for Intro.bik and;

for the Endgame videos.
When the encoding is finished, open Windows Explorer and go to ...\deus ex invisible war\content\DX2\VideoTextures. Delete, rename or move the original videos and remove the "New_" prefix from your new videos. That's it, stretch no more.

1280:720 Happy day, circular circles.