Am I Sending A Virus?
While is is possible you have a virus, the most likely reason you're seeing these messages from others is that someone that has you in their address book has a virus or worm that is forging the "From" e-mail address using your address.
Due to the way that e-mail was designed (many years ago), addresses can easily be forged in a "From" or "Reply-to" field, in much the same way that somebody could put your name and address in the upper-left corner of an envelope and mail it from the post office.
Determining where the messages actually came from requires knowledge of e-mail headers. If you wish to learn more about viewing and deciphering them, you can start here: