Dubbed Dead Rising 2: CASE ZERO, the Xbox 360-only download is meant to bridge the gap between the original and the sequel.

Explained Capcom:

Ahead of the full game, Capcom will release original downloadable content exclusively on Xbox Live with Dead Rising 2: CASE ZERO. This Prologue consists of unique content not available in the full retail release of Dead Rising 2 will introduce new protagonist Chuck Greene as he and his daughter find themselves caught in the desert town of Still Creek that has been overrun with zombies. Set two years after the Willamette incident and three before the action of Dead Rising 2, Dead Rising 2: CASE ZERO will help bridge the gap between the two titles and give players a taste of the new gameplay they will experience in Dead Rising 2 as they create combo weapons, rescue survivors and take on a ruthless Psychos before making their escape.

There's been no word as to how much the download may cost or exactly when it will arrive, though it'll definitely be before August 31, as that's when the PC, PlayStation 3 and Xbox 360 editions of Dead Rising 2 head out to North American retailers.