nvode: Fixed my own problem.. to anyone else that might have this problem in the future; if your video card or monitor doesn't support 640x480 resolution, simply right click the shortcut and uncheck the 640x480 resolution option. Should work like a charm afterwards!
If your card doesn't support 640x480 you can usually add it. I don't know with ATI but with nVidia cards there's an option to it "ad custom resolution".
I think almost all cards should support that.
I usually don't have problems with GOG-releases but I guess getting old games to run flawlessly on EVERY system might be an almost impossible task.