Are you using generic Windows drivers for the monitor?
Regardless, you can edit the settings file to do it manually.
This file is located at:
Vista:
C:\Users\username\AppData\Local\Ironclad Games\Sins of a Solar Empire\Setting\user.setting
XP:
C:\Documents and Settings\username\Local Settings\Application Data\Ironclad Games\Sins of a Solar Empire\Setting\user.setting
Please note these directories may be Hidden by default. To unhide them, go to your Control Panel -> Folder Options -> View and set yourself to view hidden files and folders.
