If your e-mail address has found its way into a spammer’s database, there is practically nothing you can do to get it out again. However, there are still numerous things you can do to protect yourself against spam, even if you can't avoid it completely.
• Learn how to view complete headers in spam messages to make filters and rules more effective. http://www.utexas.edu/computer/spam/headers.html
• Avoid the “unsubscribe” feature included in spam messages. Most spam includes instructions on how to "remove yourself from the list.” Often, when you click on the link to unsubscribe you are verifying that you have a valid e-mail.
• Do not reply to the spam message. This also lets spammers know they have found a valid e-mail address.
• Don’t click on a link in a SPAM. Again you verify that your email is valid.
• Install anti-virus software and update it often..
• Dont get harvested. Spammers harvest e-mail addresses from Web pages, disccussion boards and news groups. Any email address posted to a Web page or used in online discussion boards will be used by spammers.
• Be wary of filling in address, phone number or e-mail information on non-secure sites. Some users create “junk” e-mail accounts with a free service to use on Web forms so their real e-mail address doesn’t receive large amounts of spam.
Also, don't share any information on a site that is not secure. A secure site will start with "https" and will display a locked padlock in the status bar at the bottom of the browser window. (Please note: In Microsoft Internet Explorer, the status bar may be hidden. To view the status bar, go to the View menu and select Status Bar.).
• Use rules and filters in your maill application to screen unwanted mail.
See How To Here (http://www.utexas.edu/computer/spam/filters/)
Or better yet get a bayesian filter