Accessing a webpage outside of a local intranet

Ok, here is the problem. I have a site that I have written using PHP 4.3.9 which is running on Apache Server 2.0.52. The problem that I am having is that I am able to access my site from the local intranet, but when I try to access the same site from anywhere outside of the intranet, like my home, I am unable to access it. I always receive a message saying that my server cannot be located. Any suggestions? Also, my server is set up to accept requests on port 80 (the HTTP port) so I know that this is NOT the problem.

Thanks in advance, Matt.

Are you using the external ip address of the server? (instead of 127.0.0.1, localhost, or 192.x.x.x)
You may have firewall issues on the local intranet, blocking access to the server from the outside world.
Perhaps the local intranet isn't set up to broadcast to the webserver outside the intranet.