I was saw somewhere how to block access to a web site according to someone's IP number.

I have a guy who is harrasing me since we are competitors and I don't want him accessing my business site from his home, or his work.

I have his IP numbers from both locations through e-mails he has sent me in the past.

Anybody know how to do this? If I remember correctly, I think it was a javascrip that had the ability to accomplish this.