Not only was that the wrong thing to do, it was also kinda dumb. The guy in the car could have had a gun and blown you away. Anyway, get a good lawyer and hope you can bargain down to community service. I presume you have had no problems with the law in the past.
Isn't there something called a "citizen arrest". You don't have to be a policemen to do that. You just prevented a drunk kid from driving and breaking the law. I'd contact MADD.
Bargain down? From what Skipper says, there's no evidence of a crime. The DA has to give you all the evidence they have, witness statements, police reports, sworn affidavits, everything. And from what you say they have no evidence at all. Undoubtedly the punk swore out a warrant for you cause he was pissed that he was tricked into opening the door. Well, the punk may have stepped into it. If the DA finds out there are two sides to this story, most likely they will drop the charges. Unfortunately until you talk to the DA and explain your side of the case, all they have is what is sworn in the complaint.
So get a lawyer and march down to the DA together and see what they have. If they don't have anything your lawyer will know and so will the DA. Unless the kid is the son of the DA or the police chief, I'd say you have a good chance of getting the DA to drop the whole thing.
The last thing you want to do on this is to plea bargain. The elements of the crime are not there. You have a right to all witness statements and a copy of all their evidence. From what you say, no DA in his right mind is going to take this case to trial. Its a loser. They don't like to lose.