Hi again,
If you have Gold then you just have to:
  1. Go into my Computer.
  2. Go into C:\ (or whatever the letter of your hardrive is).
  3. Go into Program Files.
  4. Go into The Creative Assembly.
  5. Go into Rome - Total War.
  6. Go into data.
  7. Go into world.
  8. Go into maps.
  9. Go into campaign.
  10. Go into imperial_campaign.
  11. Drag and drop the file from the desktop into the folder. When it asks if you want to overwrite click "yes".
  12. Open up R:TW and play away!
Good luck and cheers!