Long story short, it's there but it doesn't work. Adding the /w line to the shortcut does get the game to start up in windowed mode, yes, but then the mouse doesn't work properly once I actually get into a mission - either I'm uncontrollably spinning at super-fast speeds, or I'm very slowly rotating to the left all the time and unable to shift my view to the right. Anyone know why this is the case and what can be done about that?

EDIT: I did some testing and discovered the maximum resolution, 1600x1200, doesn't have this problem. Of course, the problem with that is that my primary monitor's height is only 1080 pixels, so... my actually-playable choices are either horribly-stretched fake widescreen in fullscreen mode, or losing 200+ pixels in windowed mode (for the record, I also tried 1600x1200 in fullscreen, but it didn't look any different from the other resolutions).

Found an actual solution: turns out, much like just about everything else pre-2004 that fans haven't made specific patches and the like for, the simplest answer is dgVoodoo. Forcing windowed mode through the dgVoodoo control panel works without the random spinning. Only issue is custom resolutions still don't work, since the game will still run at whatever resolution is set in the in-game menu, and if a resolution is forced in dgVoodoo that doesn't match with the in-game one then various textures start screwing up. Still, 1024x768 is more than workable.