IPNetInfo is a free program that will help you find information about an IP address: The owner of the IP address, the country/state name, IP addresses range, contact information (address, phone, fax, and email), and more.

This utility can be very useful for finding the origin of unsolicited mail. You can simply copy the message headers from your email software and paste them into IPNetInfo utility. IPNetInfo automatically extracts all IP addresses from the message headers, and displays the information about these IP addresses