Does this game have widescreen support? THX

Indeed it does. I run the game at 1280x720 resolution, which is 16:9 aspect ratio, if that helps you.

Anyone tried it at 2560x1600? I'm used to playing old games scaled (320x200 is especially fun on a big monitor) but this game would look fantastic at a really high resolution.

http://www.widescreengamingforum.com/wiki/index.php/Gothic
They tested it up to 1920x1200 and it worked fine, except for the vert - . Take a look at their advise how to change to a custom resolution for your 2560x1600. It's worth a try, even though they haven't listed it.

Turns out it doesn't work; the game bails with an error dialog, probably because it can't allocate a surface that large. I don't think old directx versions supported such high resolutions.
Ah, well, looks nice enough at 1920x1200, although the scaling makes the fonts look blurry. Not a huge deal, really. WIth the framerate unlocked everything is almost eerily smooth, even with every graphics setting I could find turned all the way up. That's the benefit of running old games on a modern system.