Need some input on what to do about my insolent, rude and disrespectful son

A few weeks before my son turned 18 (2 Apr 09) he was caught with drug paraphernalia, knives and some seeds and stems of marijuana.  He was suspended from school and was given a referral to ADS which yielded a positive result for marijuana.  He is being home schooled to finish his diploma, since he is a Senior, but refuses to do the recommended Out-patient Substance Abuse Program. I am concerned about this because the paper from the court stated that if the informal hearing fails for any reason, they could authorize a petition setting the case for court, which I believe would cause him to have a criminal record. All he does with his waking moments is hang out with the other students who were caught and suspended with him and as a result we rarely see him except when we have appointments and the home school teachers come to teach.   I am so afraid for him right now.  It appears to me that he has multiple personality because sometimes he will talk to me and other times he will be down right disrespectful and rude like he has a chip on his shoulder and the whole world should revolve around him.  I do not want to put my son in the street but at this point I do not know what to do.