I am trying to install the DotNetNuke server behind a firewall (for security purposes) When it is behind the firewall, Nobody can access the websites, When it is in front of the firewall everybody can get to the websites. I have the firewall properly configured and I am changing the IP address appropriately. Any body have any clues as to what is happening?

Sorry, could not resist not joking.

Your problem might be simple to solve. Your server is behind the firewall. I consider that you are used to call it like http://server

1): Are you able to access the server using a client which is behind the firewall?

No: The problem is not firewall related.
Yes: Move to 2).

2): Do you have published your server? This could be done on multiple ways. If you have a simple port filtering firewall, you need to forward the port 80 of your firewall towards the port 80 of your webserver.

3). How do you try to access the server? Try to open http://firewall or "http:/PublicIpAdressOfFirewall"

4) Publish a DNS alias entry named "Server" pointing to your public firewall ip on your public DNS server.