Instructions
Go to the Star Wars Battlefront Files website (see References).
Select "Star Wars: Battlefront II" on "File search" in the upper left-hand corner. Type in "maps" on the search query and click "Search"; or you can go to "Browse files."
Select the maps you want.
Download each map individually.
Go to C:\Program Files\LucasArts\Star Wars Battlefront II\GameData. This is where "Battlefront II" is typically stored unless you installed it elsewhere.
Extract the files you downloaded and drag them to C:\Program Files\LucasArts\Star Wars Battlefront II\GameData.
Run "Battlefont II." Click "Instant Action." You will be able to select your new maps.