Thanks for all your help. I have downloaded Mailwasher and have used this frequently to try and bounce the virus e-mails. This seems to be working to a degree but I continue to get suspect mail everyday.
I have run Norton Antivirus again and again with the system restore on and off and these havent picked up anything. I have also used the online virus scanners as well so i'm pretty sure there isnt a virus present. I just cant seem to prevent these e-mails being sent.