Spam email (spyware) problem

For the last couple of days I've been bombarded by emails infected with a trojan. My anti-virus software has prevented it doing any obvious damage, but I am unable to stop the spam returning. I have tried Ad-Aware, Spyware Doctor, and Microsoft's own Anti-Spyware program, and none of them has helped. Curiously the addresses sending the spam appear to be my own. e.g. [email protected] or [email protected]. Does this seem familiar to anyone? How can I stop the spam?

FYI, I am running Avast On-Access Scanner and Zone-Alarm Security Suite.

Thanks.