Could this be someone who actually shares the same name as you? Or is it someone who is faudulently trying to impersonate you?
Who is the ISP involved (hotmail, yahoo, freeserve etc) as they may be able to help if you aproach them regarding fraudulent or emabarrassing mails.
Other than that, you could let everyone on your address book know about the problem and make sure they know that the emaila ddres that appears to be yours is in fact not so.