We could use a central file system remotely accessible, like webspace with SVN (subversion) folders
http://subversion.tigris.org/. Otherwise it will be really difficult to keep track of everything.
http://tortoisesvn.net/about Using TortoiseSVN would mean everyone would be working on the same XSI project folder/workgroup directory, everything could be neatly organised, backed up/versioned and everyone could remain current with a couple of mouse clicks in Windows Explorer. (It's possible there is a Linux equivalent that might work with this but I'm not sure. Is anyone going to be using Linux for this?)
Video about how it works:
http://www.vimeo.com/8370887 (Not watched it all but it looks like it shows how it works at about 1m20s).
And we could also use a bug tracker to create a list of tasks, assign people these tasks and keep an eye on what everyone is doing (or not doing

), also put on the same web server or even on the si-community server?
http://www.mantisbt.org/demo/my_view_page.phpIt works pretty well for the Black Mesa HL2 Mod. But it will probably cost money (renting server space) to do it this way.