I've got a question for y'all.

Some idiot finally sent me a junk e-mail message that I couldn't do anything about with what I have the knowledge to do -- reading the headers turned up only one ISP, which was apparently owned by the spammer.

I'm hoping you guys would know where I could find out more about this individual -- I'm hoping that he does in fact buy his service from someone else, and if so, I'm not sure how to find that out. If he doesn't, is there anything I can do?

His traffic has to be routing through somebody or multiple somebodies. Traceroute it and complain to the upstream site. Unless they're cretins like CIX they'll kill his connection.