Dark Horizons reports that Roger Avary and fantasy author Neil Gaiman will team up to write Silent Hill 2. This comes from an interview with Christophe Gans on DVD Rama, a French site, who states that Avary will work on the project after he completes his work on the Driver script.
Christophe Gans is currently working on a live-action Onimusha adaptation, and as per the article, may or may not work on the Silent Hill sequel.
Update: Neil Gaiman has refuted his relationship with the project through a post in his blog. He states that this is a discredited internet rumor, but does not blow out the possibility of him working on the project if an offer is given.