Anyway, I have come across an organisation called The Ecology Building Society. They lend money for eco-building projects, housing co-operatives, and such like. Here's a link to their mortgage leaflet for housing co-operatives - clicky!
Another site worth looking at is Radical Routes. It is a network of housing co-operatives. There's loads of info on here about how set-up a co-operative. Legal structures, etc..