where do i sign up 
You can sign up at the SCU forums, but you’ll have to read the rules first there, otherwise you can’t register.
All progress happens over there, so if you want to help out, that’s the place to be 
This is just a fan forum, not so usefull right now, but it will be usefull when the demo comes out.
What type of work is needed right now?
A bit of everything. Music and sprites mainly, as far as I understand.