You're off topic for this forum, which is dedicated to Windows Live OneCare.
What is probably happening is that a spammer has used your address as the forged "From" address in the spam. There is nothing that you can do to prevent this, short of never revealing your email address to anyone.
If, however, you believe that your email account has been compromised, contact your ISP or, if it is a Hotmail address, Windows Live Hotmail Support at http://support.live.com
-steve