From Original War Support Wiki
Tutorials -> Mod Directory
The "mods" directory can be found in your Original War directory (Commonly C:\Program Files\Virgin Interactive\Original War\). If the "mods" directory does not exist you will need to create one. You can use the Editor to create a mod. If the "mods" directory exists and you have created a mod then your mod will be found in the "mods" directory under the "short name" you entered in the Editor. When you see %MODDIR% in a tutorial it means replace with your mods directory.
C:\Program Files\Original War\Mods\MyMod\