Howtoforge posted a guide about setting up virtual hosting with Virtualmin on CentOS 5.1

This tutorial shows how to set up a CentOS 5.x server to offer all services needed by virtual web hosters. These include web hosting, smtp server with (SMTP-AUTH and TLS, SPF, DKIM, Domainkeys), DNS, FTP, MySQL, POP3/IMAP, Firewall, Webalizer for stats.

Virtual Hosting Howto With Virtualmin On CentOS 5.1