Given the person who mentioned this, we can consider this more credible than your average rumor. At this weekend's C2E2 convention in Chicago, a number of stars from The Walking Dead participated in a Q&A panel and Laurie Holden mentioned that Stephen King is currently in talks to write an episode for the second season.
Since Frank Darabont directed King's Shawshank Redemption, The Green Mile, and The Mist, this sound like a definite possibility, and I think both fans of Stephen King and The Walking Dead will be happy to see him write an episode. For more season 2 information revealed during the panel, check out the source link below.