NOTE: This file has been updated to version 1.06.3, which was recently pushed to Steam. This modified executable allows you to select any resolution your graphics adapter actually supports within the game, including full HD etc. The game interface works just fine with the modified resolutions. I have only tested this mod for the Steam version. To install, simply replace your old executable. Preferably you would create a backup before doing so. See Description for technical details.
Technical details: By default Act of War correctly detects all your resolutions, but filters them for resolutions which have an aspect ratio of 1.25 or 1.33. This filtering happens during UI-setup (after the strings for the menus have been allocated etc.).
The filtering code can be found by searching for the string TAOWSubOptionGraphicConfigurator_NotCreatedObject (Ascii). A few bytes after that, you will find the pattern 83C4F489542404DB442404894C2408DB. Replace the first three bytes by B001C3 (opcodes for 'mov al, 1; retn'). For the current steam version, all this can be found at 0x5AE3FC.