NOT detctable Spam mail Server Problem

I am getting 4-10 emails daily from different domain names with subject “delivery status Failure”. Which I have never mailed to. Now I have Norton Internet Security 2003 and other Antiviruses as Onguard. Though I have doubt that some sort of SPAM mail server have been installed on my Desktop I don’t have any Idea. The problem is its not getting detected and I don’t want to Format my Partition. Also I have scanned it with different spyware detecters like spybot, McAfee and others…. But NO results. NOW THE QUESTION IS: HOW DO I “DETECT” THIS THING AND REMOVE FROM MY DESKTOP WITHOUT formating my partition ?