problems with e-mails

hi folks
i seem to have a problem with my e-mails. i sent an e-mail to a friend and he told me that he got 6 copies of the same e-mail . i am also getting e-mails returned to me from people that i have never heard of .
i was wondering if this could be one of these e-mail bots that i have heard about that just pump out e-mails .
i have avg 6 antivirus which is upto date with updates . i am using sygate firewall also upto date . i have scanned with ad-aware . and spywareblaster .
i have also done scans with giant antispyware. also spybot search and destroy. they have not found anything .
so if i have got a bot in my system how would i go about finding it and getting rid of it . i should also say that i am using xp pro.

thanks in advance baccyman

You use outlook?

Check which accounts are 'installed'

i am using incredimail . i have had a look at the block sender and there is nothing in there . and i have got the spam blocker active which as far as i know just stops the e-mails going into my in box.