What are you still doing reading this? You don't even need to read this! The map pack is out! Go get it! We can't play it because we're at work, but you can!
UPDATE: Xbox Live seems to be having "issues" currently. Our best guess is that lots of people (like everyone at G4) got home from school/ work and is trying to download the same map pack at once. These issues also extend to the forced download on the CoD4 system update, which means no online play until you get thru. Sad face.
UPDATE v2: Keep trying over and over... took us about ten minutes of refreshing and retrying the download to get it to start. See you online.