Your problem is that in fullscreen mode there is a big black border around the game screen?
That is because you're display doesn't scale the picture. Possible solutions for this would be:
1) See if you can get your graphics driver to scale it, some have support for. Look it up in the manual or use Google.
2) Set ScummVM to scaling. To do this most esaily, edit your Broken Sword 1 shortcut (right click -> Properties). Doesn't matter if you do this with the Desktop or Start Menu shortcut. Delete the "sword1" (without quotes) at the very end of the Target field. Click Apply and launch the game using the shortcut you've edited. You are now in the main menu of ScummVM that you don't normally see as GOG launches the game directly. On the right is the Options button, click it. You are now in the Options menu, in the graphics Tab, exactly where you want to be. The the dropdownlist right at the top labeled Graphics Mode is where you can set ScummVM to use one of the builtin scalers. You can read about the different scalers [url=http://wiki.scummvm.org/index.php/User_Manual/Appendix:_Graphic_filters]here[/url], with comparison screenshots using Maniac Mansion. Buit you'll probably want to experiment around with them a bit because such things are highly dependent on the game and personal taste. If you don't find a setting that's big enough (maximum is 3 times the original resolution) I'd use a scaler you like an set it to windowed mode. When you found a setting you're comfortable with re-add the "sword1" to your shortcut right where you deleted it.
Sorry for the wall of text, but I don't think it is explainable shorter, it is a bit complicated, but shouldn't be all that hard with my instructions. Feel free to ask if there are any more questions or problems.
Post edited October 02, 2011 by Gabelvampir