Computer crime that crosses U.S. state lines falls under the auspices of the FBI. It's also possible that your state or local police might have a cybercrime division, although these are often severely lacking. (In my own state, Pennsylvania, for example, the state police cybercrime division is limited to investigating the trafficking of child pornography.) You can find the address and contact information for your local FBI field office on the FBI's Web page, www.fbi.gov.
The National Infrastructure Protection Center http://www.nipc.gov/ is a federal agency designed to protect the digital innards of U.S. business, industry, and education.
You should report the crime even if you do not intend to pursue it. This gives law enforcement officers valuable statistics about the nature of crimes being committed and their frequency, and will help them spot trends. At the very least, you should fill out a Cyber Threat and Computer Intrusion Report, which you can do on the NPIC Web page.