sethsez: Well the aspect ratio looks correct so I don't think it's been stretched, and Cinemascope isn't actually widescreen, it's just 4:3 that renders the top and bottom of the screen as black bars. If you're using it and try to access a menu, the menu actually goes into the black space.
Oh, I see. I just gave it a try, and while you're right, at least the normal HUD is not inside the black bars. So, maybe whoever took that photo of Outcast running in widescreen was really able to play it like that and just had to bear with the menu being cut off a bit.
Judging from how problematic it already is to get the game to run without black borders, and how 640x480 seems to be the only "non-standard" resolution that can be used, while even that doesn't work flawlessly, I can't imagine that it's possible to run Outcast with a proper widescreen resolution without problems.
Loengard: And how would you do that? It seems I can't get it stretched. It's just tiny window with huge black borders on every side of my screen.
Using one of the methods mentioned in this thread. Apparently it doesn't work for everyone, but I got the game to run in 512x384 without any black borders, thus enabling my display to stretch the image to fullscreen.
Though, as sethsez said, if you have a widescreen monitor and the image gets stretched to fullscreen, it should look rather distorted.