View sites behind the router

I have set up a Centos Web host mail server. It serves about six sites from the one IP address using Apache. Nothing new.

It sits behind a router which obviously turns the public IP into a private one. So when you type in the private address of the server (when you are on the private LAN) the first site in httpd.conf appears.

What i wish to know is. How do i see the other six sites on my browser if i am behind the router on the private IP range? If I try using the www address it cannot find the site.