A person has filed a law suit against another party. I have a promissary note where he promised to pay me back 1200 dollars.

I wouldn't bother sending it.  Unfortunately, it won't be that simple to get the money as the lawyer has no right to issue money to you from the other lawsuit proceeds (that is, assuming that your promissory note doesn't have anything to do with the other suit - like being an expert witness or something).  What you'll want to do is go directly to the person and demand the payment per the promissory note.  If he decides not to pay you, you can file a lawsuit in small claims court.  Either you'll settle it out before trial or (if things go your way), you'll walk out with a Judgment that allows you certain rights to collect the money.