Any decent firewall will be able to log attempts made by peps to gain access through certain ports or there are programs speacily designed to act as trojans sitting on the default ports and waiting for peps to connect - these progs shoul also be able to log any attempts made.....simply note down the date/time and ip of the person attempting to amke the connection and email them off to your isp - they should be able to take it form there.

Either that or they'll ignore it - well thats wht they usually do