rpc over http

I have set up rpc over http on a single Exchange server sp1 according to MS in their KB but I cannot get it to work properly for some reason. I cant get Outlook to find our mail server over http and I think it might be a firewall issue. What ports do I have to open up if any on our external firewall other than 80?
If Anyone else has suggestions on what I am missing or done wrong, please let me know.
This server is an Exchange 2003 server with server

Thank You