TO INSTALL IN VISTA:
Copy folder to -
C:\Users\*YOURUSERNAME*\AppData\Local\Ironclad Games\Sins of a Solar Empire\Mods-Entrenchment v*VERSION*\
Launch the game, Options, Mods, Enable Mod, Apply Changes.
TO INSTALL IN XP:
Copy folder to -
C:\Documents and Settings\*YOURUSERNAME*\Local Settings\Application Data\Ironclad Games\Sins of a Solar Empire\Mods-Entrenchmentv*VERSION*\
Launch the game, Options, Mods, Enable Mod, Apply Changes.
Replace the info surrounded in asterisks with your info. If not entrenchment, just stick in the Mods folder of that directory. If you cannot see these folders, you need to edit your folder options to Show Hidden Folders.