Well, admittedly I've been away the last few days, and I see you've already got a lot of support here... Just remember, you'll always have us, I REALLY hope things get better for you...
That said, have you considered moving out and finding somewhere of your own? Even if you actually showed your intentions then maybe they'll start giving you more of the respect you deserve if they think you're serious about it... I guess it must be hard for parents to see their children grow up... perhaps you need to help them realise that you aren't someone they can tell what to do any more...
Either way, I wish you luck...