A perl interpreter is actually compiled into the httpd binary. Most popular reason for using is to speed up execution of CGI programs. FastCGI is a different way of speeding up the execution of CGI programs.
Programs are faster because they are used for multiple request instead of just one.
In essence, they become daemon processes, and the webserver connects to them as needed. FastCGI is dirt simple and just as quick. FastCGI has fewer users and less documentation. Virtual hosts are a way of using one instance of Apache to host multiple websites. BindAddress and Listen directives control which IP addresses httpd will communicate with.