How do I trace an I.P. addy?

I have a piczopage where people can leave messages to me. The problem is someone keeps leaving obscene messages to me.I have to approve the postings before they can go on but this person knows I read them. I wote the I.P. addy down and went to WHOIS but all it told me was they were using AOL. am I doing something wrong when I go to WHOIS? By the way the I.P. im hunting is 64.12.116.132 any help would be most apreciated.