How do I make money off of this AJAX chat script I made when the client defaulted on the payment?

Take this as a 'lesson learned'. When you do work for the next client, be professional about it. Quote him, have him accept the quote, then get paid 1/3-1/3-1/3. Do all the work on YOUR OWN web site, and then after he pays the first 2/3, make it operational on his and collect the last 1/3.