For those unfamiliar with The Walking Dead, here's the summary:
The Walking Dead is centered on Rick Grimes, a small-town police officer from Cynthiana, Kentucky, his family, and a number of other survivors who have banded together in order to survive after the world is overrun with zombies. As the series progresses, the characters become more developed, and their personalities shift under the stress of a zombie apocalypse. Fighting growing despair — and sometimes each other — the group searches for a secure location which they can finally call home.
Personally, I'm trying not to get too excited about this yet; I've been burned by too many casting rumors in the past. And it's something I'm likely to watch even if JB isn't cast in it. But it IS exciting - I'm a huge fan of the series and an even huger fan of Darabont, who IMO is a genius as well as a lovely, lovely man. (Met him at a screening a couple of years back and he chatted with me at length and signed my copy of his unproduced Indy 4 script. Hee.) This would be a huge score for JB as the show has enormous buzz behind it. Now, granted it won't be to everyone's taste - the comics are beyond dark, inventive but extremely bleak and I'm sure they'll retain at least some of that tone in the series, if not all of it. (It'll be harder to sustain that on the screen than it is on the page.) Although... well, comments for the rest of the speculation. ;) GO!...
ETA: I'm hesitant to reference too many links in case they end up casting somebody else. :) But this interview with Robert Kirkman should tell you everything you need to know about the potential of this pilot, esp. if you have preconceptions about the zombie genre.