Does your Windows desktop work ok at 1600x1200?
You can try editing the config.div file in the Beyond Divinity folder in Notepad (or any other text editor), and change the resolution something else, as long as your monitor supports the resolution. The game should work fine at other than supported resolutions, though opening the automap at higher than supported resolutions may cause crashing, depending on the system and how much higher it is.
I tried editing my config file to play at 1440x1080 (which isn't standard and doesn't show up as a desktop resolution), and got the same top corner section of the main menu displayed that you described. A resolution of 1152x864 works fine (which is not supported by the game, but is by the monitor), other than the quest log border being smaller than the screen size (ie the 1024x768 graphics are used).
Are you running BD in Win9x compatibility mode? If not you could try that.
Maybe someone with Vista will have some other suggestions...