Hi,

this problem is a dosbox problem and I have it with all dosbox games from gog.com, not only DK1.
In fullscreen the screen is split in half, but the right part is displayed on the left (and broken with artifacts) while the left part is displayed right (and without artifacts). Changing display settings through the gog settings program did not help.
I have windows 8.1 64bit and the latest Nvidia Drivers installed.

EDIT:
Oh, I found the solution myself after reading more about the dosbox.conf file.
Changed the resolution from "original" to 1920x1080 and set aspect to true, rendering using opengl.
Would be nice if the gog tool would allow more options.

I would personally recommend running DK1 with KeeperFX. It will allow you to use true widescreen resolutions and it looks significantly better than the DOSBox version.

Refer to the install guide here for instructions

Thanks, I will try it out.