If installing the DansGuardian-Virus-Scripts tarball, just extract and then 
copy to /usr/lib.  Also copy the etc/cron.hourly entry to /etc/cron.hourly.

tar xvzf DansGuardian-Virus-Scripts-1.05.tgz
cp -av DansGuardian-Virus-Scripts-1.05/usr/lib/DGVirus /usr/lib
cp -av DansGuardian-Virus-Scripts-1.05/etc/cron.hourly/update_virus_scanners /etc/cron.hourly


These files are from MailScanner 4.22-4 (http://www.mailscanner.info/) and are
released under the GPL.