squire,
You can look at the full header from the email in question and get details about the originating IP and ISP that the email came from, along with all the places the bounced it off from to get it to you.
That email could have come from someone's computer that was infected with a virus and is sending emails out without the owner of the computer having any knowledge of it. Also it could be coming from a computer that a hacker was able to hack into and control in order to execute his email attack on other computers.
Here is a good explanation on what everything in an email header means:
Reading Email Headers
Take Care,
Richard