I just installed Dungeon Keeper Gold and the resolution is nearly unusable. In this case I use WinXP in VirtualBox with 1920x1080. But, however, I would like to read an easy-to-understand HowTo for the GOG-DOSBox-Configurator also for other games and other Windows-installations.

For me it looks like Direct3D works fine as Graphic mode but OpenGL does not. Changes in Scaling Engine and Window Resolution seems to have no effect.

How does the GOG-DOSBox-Configurator work?

Does nobody know how the GOG-DOSBox-Configurator works?

Well, with the silence I guess that's your answer. :)

Personally I do not use is and edit the .conf directly.

http://www.dosbox.com/wiki/Dosbox.conf

The thing hindered me from modding a game so I ripped it out and deleted it for that game, otherwise just using DOSBox conf like Strijkbout. It takes a while to learn but then it gives you more options and they work on games not from GOG too.

Is your problem by any chance that the game runs in its 320x200 resolution (meaning it looks more or less like the first picture attached to this post)?
If so, that's just how the game looks by default and no tinkering with Dosbox's cofiguration will change that. The "window resolution" option merely controls how large the Dosbox windowed mode is, if you don't run it in fullscreen. However, it doesn't have any bearing on the actual in-game resolution, it just scales up the output.

Although, Dungeon Keeper does have a built-in "high-res" mode (640x480, see picture #2), you can only access it by pressing ALT+R while you're in a level of the game. The game will remember this setting, at least if you make a save file.
Unfortunately, there's an issue with that. Dungeon Keeper (like a lot of other Bullfrog titles, such as Theme Park) reacts heavily to the speed of your processor. Unless you set a fixed "cycles" count in Dosbox to limit its speed, the game is likely to run way too fast on modern computers.
GOG had to set it to 80000 cycles to accomodate the default resolution, but that's too slow for the "high-res" mode. You can either press CTRL+F12 in-game to increase the cycles until you have a satisfying speed (CTRL+F11 decreases the number), or you can go to the "dosboxDK.conf" file and change the "cycles=80000" entry to whatever value is appropriate (because Dosbox doesn't remember the setting via hotkeys once you exit).