In my divorce decree, 6/20/2002. My ex-husband was ordered to pay me half of a debt we both owed but I paid. He was ordered to pay me $100 a month until paid in full, a little more than 5 years. As of today, 10/11/2010, he has paid $1,200.00. How can I collect the balance of what the court has ordered?

I'd see an attorney. See if you can collect the money and interest on the money he's failed to pay.