Rules would be simple: Every week, there's a theme, and people make a song (original, remix, WIP, w/e) around that theme, upload it, and post it to a forum (possibly a different site meant for this purpose), then at the end of the week everyone gets together in a chat room and we do a sync listen (p much a host would tell you when to queue and start a track).
The idea is to drive people to create music more regularly, so they don't fall out of practice, and to be able to get constructive criticism. Also fun I guess. These things are fun.