Hi,
Download the free smartcop virus scanner from the site www-s-cop.com. Disable Avast and run the smartcop virus scanner and see if it is able to clean or delete your infected files.
You could also try nod32 for dos from the site www.nod32.com.
Make sure you disable Avast when using another antivirus. I heard that Avast will create problems when you try to install another antivirus when it is resident.
This is the same answer that I suggested to countryboy also.
Regards,
Balaji.