The 1.15gb download is ready for download to Xbox Live users. If you already have the World at War maps, you are entitled to Moon free of charge. To get it, simply select Xbox LIVE using the LIVE profile originally used to redeem the maps. Just look for the Rezurrection AD and click on it, then click on re-download (it will ask if you want to redownload again).
In addition, Hardened or Prestige owners also get the goodies offered to the rest of us, including the Moon Xbox LIVE theme, and soundtrack. Players that haven’t purchased the Hardened or Prestige Editions, can get Rezurrection’s five maps for 1200 Microsoft Points ($15 USD).