Keep a copy of all communications you have made so far. It's easy to open a Paypal dispute, but once you do make sure all communication is done through their dispute console, i.e. - don't do any more direct e-mails / phone calls or PM's. If the other person fails to reply through the console after x days, and you show that you have made all reasonable efforts to resolve the dispute, then they should find in your favour and take the money back from the sellers paypal account.
Hamster