Eric Langhorst has a notice on his Guerrilla Season Book Blog that the 2008 project will take place March 3 - April 4. If you want to participate (either as an individual or as a class), all you have to do is write him. The details are on the blog.
I hope to participate the project again this year. I read the book and participated to a limited degree on the blog last year, and it was a great experience. The author, Pat Hughes, interacted with Langhorst's 8th grade students on the blog. This year he is promising new features, and I am sure they will be exciting!
I would encourage you to follow the project even if you don't want to participate. (The book is very interesting, though. I really enjoyed reading it.) The blog they will be using this year is http://www.guerrillaseason2008.blogspot.com/. It isn't really up and running yet, of course, but it will be before long.