I agree with this...basically show him where he's headed if he doesn't straighten up. Show him that it costs him more than he realizes when he doesn't listen to you. Do you pay for all his shit? Stop. If he wants something other than food that's already in the house or food when you go out to a restaurant as a family, its up to him to come up with the money for it. Also take away the computer period at least for a month or until things start changing with him. There is probably a library at school with plenty of computers available for him to do homework on, and they likely won't let him spend his time on myspace. Most teachers wouldn't consider not having a computer at home a good excuse.
Be harsh by forcing him to man up