From following the link at the bottom of the page to the official site:
Requiem v2.3 full release
- This version should work with your existing v2.x Requiem save games
- Copy this full release ZIP to your Mods-Entrenchment v1.03 folder
- Before extracting this ZIP file you can delete any existing Requiem directories in your mod folder.
- UnZIP it there.
- You can verify the installation by checking your checksum has been updated to 31433096
To elaborate on some of those, though:
You can find out where your Mods folder is by launching the game, going into Optioins > Mods and then Show Mod Path. It varies slightly depending on your OS (Windows XP or Vista).
Make sure you have "Show hidden files and folders" enabled in Windows Explorer (Tools > Options > View tab > select "Show hidden files and folders") because the mod path is usually hidden.
Then just download that file, put it into the Mods-Entrenchment v1.03 folder and double click it to open it up. Inside yuo'll see the actual mod folder. Select it and then there should be an "Extract" button.
Once you do that, just start up your game and go back into Options > Mods and it should show up. Select it there and hit Enable and then it will give you the Checksum number that you can use to compare with the number given above to make sure nothing is missing.