httpd conf advice for a newbie

Hi, i have set up a pc running windows 2003 server. I have installed xampp to give me apache, php, mysql etc. I am now at the stage of having had my domain name pointed at my ip address and ports opened etc and have to edit the httpd conf file but am finding this diff. I am able to view my test page as localhost or 127.0.0.1 but not access it via the internet therefore I am assuming I have not edited the httpd file correctly. Can anyone offer advice as to what the basic changes are that i need to make or point me at an easy to use site or book that i can check it up on?
many thanks.

Is it possible you have a router or firewall blocking access to the port?

Are you trying to access your server using your external IP address, or your domain name?
Your domain name may not be fully setup; try accessing with your external IP address

Thanks for the reply.
According to isp, all is set up.
I have tried accessing from domain name and ip address.
As a school we have an external firewall which our isp runs - this has been deactivated (supposedly) but i have not checked the router in our office yet.