Once the webmin module is installed you need to config the module to point to the relevant files and directories.  Assuming a default install on a redhat based system the following settings should be used:

Full path to MailScanner Program = /usr/sbin/check_MailScanner
Full path and filename of MailScanner config file = /etc/MailScanner/MailScanner.conf
Full path to the MailScanner bin directory = /usr/lib/MailScanner
Full path and filename for the MailScanner pif file = /var/run/MailScanner.pid
Command to start MailScanner = service MailScanner start
Command to stop MailScanner = service MailScanner stop