DNS/Firewall prob

We have a 'no nat' router and a firewall doing nat for us. All our machines inside our network are statically assigned IP's. Our webserver can be seen from the outside no problems as there is a route open on port 80 for that machine from inside the network... However, if we try to view the webserver from inside the firewall using its external address, the browser times out. Our ISP and Firewall vendors both conccur that we either need to use local DNS or a HOSTS file to locally resolve the name. Although fairly techy and competent, this seems a bit of a grey area for us as no one seems to be able to shed any real light on our problem. Any ideas anyone? Thank you anyone in advance! Dan...