The Times recently had a great piece about cohousing, after a visit to the Community Project. Well worth a read.

It also talks about getting started, and mentions that:

Alan Heeks’s advice for those hoping to follow in his footsteps is to start small. “You need a fairly focused core group of 8-10 people who communicate well and can keep up the level of commitment,” he says. “Then you can widen it out and bring in other residents.” You should also do your research and visit local schemes before starting.