Sorry, been off about and not on here for a few days. Hope I'm not too late to tell you some useful stuff. you should definitely get yourself acquainted with the Cowley Club,
http://www.cowleyclub.org.uk/ i am pretty sure the website tells you all you need to know. You'll find all manner of useful people there. With regards Housing co-ops to live in I honestly don't know of anything useful. i have been housed up for a whole fucking year now, due to health and legal bullshit so i am not fully out there with the knowledge. If I hear of anything I will be sure to let you know. But i truly believe the Cowley Club can help you in your search. Another useful place in Brighton is this place
http://www.bucfp.org/. don't be put off that it all seems for families and kids and that. it's really not. You can do washing there, get really cheap vegan meals, free clothes, cheap if not free internet, its warm and safe and all the people there are good, nice people. They also do loads of group/education things like art groups and learning languages and you can get impartial welfare advice re: benefits or legal shit. Its a useful place to go if its cold and wet outside. There is also this place,
http://theclocktowersanctuary.org.uk/ I don't know how old you are, so you might be out of their age range, and I am not saying you need half the help they offer, but I know you can get food and free internet and shit from these people, so might be worth looking up if you are young enough!! I haven't personally had dealings with them as been too old for too long!
Also, i was wandering the internet the other day and saw this
http://uk.cameloteurope.com/508/0/available-properties/available-properties.html
I know some people are dead against this whole property guardian thing as its essentially fucking over squatters, i am in two minds about it. i did notice that they had a property going in Brighton. Its still £500 a month which is a lot, but i am not sure what you get for your money, but might be something to keep an eye on.
Oh yeah, you asked about the punk scene. Do you know what, i am embarrassed to say, but I don't really know, its not something I am particularly into myself. I know they have a punx picnic in brighton and I know the Cowley Club put on a lot of Punk nights, but that is about the level of my local punk knowledge. sorry.
I feel like I have just provided info for a worse case scenario if you came to Brighton. I will have a better think about where all the cool/like minded people are.
laters...