As mentioned above, setting up services (ie. POP/SMTP, FTP) for certain virtual servers is very flexible. You can specify whether vserver2.com should have FTP service, or if vserver1.com should have email. I am going to cover the basics of how to set up virtuald through the common services.
Basically for each service in your inetd configuration file, you want to add: /path/to/virtuald virtuald /virtual/conf.file
But, if you are using tcp_virtuald, you will want to use: /path/to/tcp_virtuald virtuald /virtual/conf.file tcpd
For xinetd, please read the section below. It will still be helpful not to skip this section...