Hi Jim,
Unfortunately you can not force someone to stop using your email address as the From: address on their emails.
Do you have an email from them? Can you get the
full email headers?
With the full email headers you can get their ISP / IP address and from there you can submit an abuse report to their ISP to have the spammer shut down.
Another solution you can implement today is an
SPF Record that will let other email providers who check SPF know what the legitimate sources are for email From: your domain.
-Raymond