I would recommend a shared blog so each person can share current notes/ideas/links- for ideas and brainstorming. This is the place for peer comments and discussions. I can edit a blog post easier than a sent email.
A wiki would be great for separating known and unknown answers to the questions that arise during the project. This is the place to show what has been done and what needs to be done. Discuss these topics on the blog, not on the wiki 'discussion' page; post the _results_ on the wiki.
org-mode or something that simulated it would be great for prioritizing tasks. For those that are not familiar, it is an emacs mode that, among other things, allows you to create and move nested lists ( lists of lists ). This is the place to micro-manage the order of steps so that they are done most efficiently and keep people on track.