is this a virus?

hey all...i'm about to run thru Read Me & Run First steps for spyware/virus detection removal, but i'm not sure if i actually have a problem.

the only signs of a problem i see is that i keep getting "returned mail - undeliverable messages", indicating e-mails containing viruses are being bounced back to me from addresses i don't recognize. but i have been told it is possible that my address is being spoofed elsewhere, so while the bad ones are returned to me, they are not actually being sent by me. since i have disabled scripts and run AVG and the anti-worm stinger with no virus found, i assume this could be a possibility. is it possible for bad e-mails to come back to me when i did not send them? or is the problem really in my pc?

thanks for any help - i'm going to run through the detection/removal sequence posted here, but i am wondering if i might be chasing shadows?

Hanna