wow that's an interesting problem you have . . . do you have a static ip by any chance? (just a guess, i'm in the dark here). Have you tried ad-aware?
edit: i read an interview with a famous spammer who wanted to be able to do just that to your computer--at the time it sounded about like zapping a computer with a mars-based death ray--but it seems a little likely right now. I don't suppose you have multiple partitions or harddrives and just formatted one of them? Otherwise i'm in the dark, and the only suggestion i can make is ad-aware. No chance you got the same bug from the same email?
edit2: ha i knew there were learned people here.