Here are some command-line arguments I found for "Project IGI 1 Demo", I have only tried these with the demo so I don't know if they will work in the retail version of the game.
To set a command-line argument right-click on the desktop shortcut of Project IGI Demo, choose Properties, in the Target-field write a command argument after the filepath, so it will look something like this: "C:\Program Files\Eidos Interactive\I'm Going In Demo\pc\igi.exe" Window (which would start up the game in windowed-mode).
- Window - Start game in windowed mode
- NoLightMaps - Affects graphics
- NoTerrainLightmaps - Affects graphics
- Debugtext - Print some debug-information in top left corner while playing a level.
- WinInput - ???
- Germany - ???
- LevelX - Start level X (where X is an integer). Eg. Level1 would start the first mission.
- UnlimitedAmmo - Unlimited ammo.