The GameStop page is showing GTA IV DLC The Lost and Damned as a boxed product for $20.
Apparently the packaging will include “a 2 sided poster and an Xbox LIVE Marketplace token card. The token card will contain a unique code to purchase The Lost and Damned over the Xbox LIVE Marketplace.”
There’s no disc inside the pack: just the token to get the DLC. And you’ll need to have the original game to download it, obviously.