Welcome to the Org Zeus
  1. On your RTW main menu (the first one you see when you enter the game) click on Multiplayer.
  2. Click on enter CD Key.
  3. Find your R:TW manual and look on the back cover. There you should see your key in an area labelled "Key Code" or something similar.
  4. Click on the green tick.
  5. Play multiplayer as normal
Good luck,
Avlvs