The reso is 1:1 scaled to your display resolution setting.

e.g. If your system resolution is 1920x1200, and you resize the demigod window to take up one half of the screen (an A4 page) it will now be 960x1200 (obviously height is actually a little less because of start bar and top bar).

Quite sure that's correct?

I started using windowed mode so I could desktop without crashing... But whilst actually playing games I seem to be crashing more frequently.

What you can do is attach a command to the target field of the shortcut. This saves time if you want the game to start in a certain resolution in windowed mode. It should look something like:

"C:\Program Files\Stardock Games\Demigod\bin\demigod.exe" /windowed 1280 720

The funny about this is: Everytime i resize the windowed game, it will crash with no message.