If you would . . try setting the res at 800 x 600 to see if the game will give you access to the menu buttons and allow game play. That is what most folks using netbooks with a 600 vertical res have had to do in order to play the game. You should be able to use the "Configuration" icon that is in the game menu (Start,Programs, GOG, Divine Divinity) or right click the configtool.exe located in the DD install directory, click "Run as an administrator" and select 800 x 600 from the dropdown.
If you have installed the game in Program Files Windows may block you from editing the config.div files. You might try turning UAC off temporarily to see if you can edit the file. Sometimes you can copy the config.div file to the desktop, edit it, and copy it back into the DD install directory confirming an over-write (keep a backup copy). I would suggest you install in a directory outside of Program Files (see the install tips post ) if you cannot edit the file. I assume you are using an admin account
If 800 x 600 stretches / distorts the screen too much you may need to right click the game shortcut, click properties, click the Compatibility tab and disable some items. (see attached) Depending on your video card you might also need to disable scaling. The option is different for every card so you might have to hunt for the option. See the Nvidia Control Panel in the attached for an idea of what the setting might look like.
Edit: BTW, it is only the start screen / menus that clip, the game itself will be at the selected or manually set resolution. Only the fact that you can't see the "OK" buttons make DD unplayable. If you had gotten into the game itself you would see that it fits the monitor correctly . . =)
If you turn UAC off I would suggest you turn it back on after you get the game running.