I don't know if this has happened to anybody but me, but I want to put this instructable out there for anyone who might need it. I recently downloaded the Rezurrection map pack for Call of Duty: Black Ops and the Season Pass and Nuketown Zombies for its sequel of the same name, both on XBOX 360. A problem I noticed that was recurring was that it never transferred the downloads to active downloads; they just kept pending. The purpose of this instructable is to help anyone out there who is encountering this same problem. PS- As far as I know, this only happens on Call of Duty games, so I will refer to my experiences downloading Rezurrection and the Black Ops 2 Season Pass throughout the instructable.
Step 1: Purchase the DLC
First and foremost, you have to buy and begin downloading the content. In Black Ops 2, you can do this from the main menu for either Multiplayer or Zombies.
Step 2: Open Home Screen
Press the green/silver button in the center of the controller to access the XBOX 360 Dashboard. Select the option to go to the XBOX Home screen, and press A. Click yes and it will take you to the screen shown after you sign in, but before you start the game.
Step 3: Open Active Downloads Screen
Next you'll want to go to the Dashboard again. Scroll over to the Games and Apps tab and scroll down to Active Downloads. Press A.
Step 4: Wait for Content to Download
Wait until everything you purchased has been downloaded. See, the key is to download the content outside the game. Otherwise, you'll be sitting in front of your XBOX, getting pissed off while your download is still pending, like I was. Don't worry if it takes a while. Nuketown Zombies is totally worth it.