Ommmward is right. I'd start by finding out what's in your area already - you may well find there are yahoo or google groups where people list activities. I've been involved in starting up a couple of home ed groups, because at the time there wasn't much going on in the area. It's not that hard. You maybe put a message out on the local yahoo group to see if there's interest, perhaps find a local venue, like a scout hut and set a date and see who turns up. There's not really much red tape - in our groups we say the parents/carers remain responsible for their own children.
Home ed group meetings can be very informal and just a chance for children and parents to socialise or you can get speakers in, hire tutors and share the cost, organise science/craft/sports activities. In our various local groups lots of different sports are available, organised by home edders who have got together; climbing, tennis, football, table tennis, fencing, horse-riding etc. There are languages taught, history, drama, maths, English, science, first aid, sign language, I.T. - almost any subject you can think of.
I was worried that the children would miss out on certain things as a result of being out of school, but through getting together with other home edders, they've done sports days, Christmas plays, concerts, Christmas parties, residential activity trips.
I'd definitely recommend trying to find a local meet up and going along to chat to home edders - I found it really useful to talk to people about their different approaches to home ed and also to see their children.